<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:d3ce27d0-a4d3-4a09-b6d6-e45072faf2fe,g:36aad011-cd51-474c-90e8-1c9d6b70b2bf-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.swgas.com/role/Cover" xlink:type="simple" xlink:href="swx-20250331.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_205e2b86-ef4b-4a32-a2e2-e761dfe181a2" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntitiesTable_205e2b86-ef4b-4a32-a2e2-e761dfe181a2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_1f4dbb33-21b4-4e33-8565-5deec3078cc2" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_205e2b86-ef4b-4a32-a2e2-e761dfe181a2" xlink:to="loc_dei_LegalEntityAxis_1f4dbb33-21b4-4e33-8565-5deec3078cc2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_1f4dbb33-21b4-4e33-8565-5deec3078cc2_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1f4dbb33-21b4-4e33-8565-5deec3078cc2" xlink:to="loc_dei_EntityDomain_1f4dbb33-21b4-4e33-8565-5deec3078cc2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_c9b3fde5-3bd0-40de-8a33-e05035945fea" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1f4dbb33-21b4-4e33-8565-5deec3078cc2" xlink:to="loc_dei_EntityDomain_c9b3fde5-3bd0-40de-8a33-e05035945fea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_734ce032-726b-4a23-8eb8-3d98b7580a13" xlink:href="swx-20250331.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_c9b3fde5-3bd0-40de-8a33-e05035945fea" xlink:to="loc_swx_SouthwestGasCorporationMember_734ce032-726b-4a23-8eb8-3d98b7580a13" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_e4997a66-aaa2-4ba4-8ad1-6250a22e8fab" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_205e2b86-ef4b-4a32-a2e2-e761dfe181a2" xlink:to="loc_us-gaap_StatementClassOfStockAxis_e4997a66-aaa2-4ba4-8ad1-6250a22e8fab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_e4997a66-aaa2-4ba4-8ad1-6250a22e8fab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_e4997a66-aaa2-4ba4-8ad1-6250a22e8fab" xlink:to="loc_us-gaap_ClassOfStockDomain_e4997a66-aaa2-4ba4-8ad1-6250a22e8fab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_19c908e9-a117-4b70-9fe6-f1f7c53341b9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_e4997a66-aaa2-4ba4-8ad1-6250a22e8fab" xlink:to="loc_us-gaap_ClassOfStockDomain_19c908e9-a117-4b70-9fe6-f1f7c53341b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_ee88404a-9347-4666-8c4a-4da64e67ddbf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_19c908e9-a117-4b70-9fe6-f1f7c53341b9" xlink:to="loc_us-gaap_CommonStockMember_ee88404a-9347-4666-8c4a-4da64e67ddbf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_PreferredStockPurchaseRightsMember_6cdb27fa-1c47-42b3-88c4-66df9699fc28" xlink:href="swx-20250331.xsd#swx_PreferredStockPurchaseRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_19c908e9-a117-4b70-9fe6-f1f7c53341b9" xlink:to="loc_swx_PreferredStockPurchaseRightsMember_6cdb27fa-1c47-42b3-88c4-66df9699fc28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_685ff955-2a38-4cde-9c05-64025f3e4518" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_DocumentType_685ff955-2a38-4cde-9c05-64025f3e4518" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_d42f5e57-cf4b-46a3-972a-0ecfd80b7159" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_DocumentQuarterlyReport_d42f5e57-cf4b-46a3-972a-0ecfd80b7159" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_e5a0749b-2782-4ce5-a586-e8ba1f2d4a66" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_DocumentPeriodEndDate_e5a0749b-2782-4ce5-a586-e8ba1f2d4a66" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_cbf50069-f22a-48ef-bb57-fdd620fa74a9" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_DocumentTransitionReport_cbf50069-f22a-48ef-bb57-fdd620fa74a9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_64cbfeef-dfcd-4d3e-b75d-3ce08724a354" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityFileNumber_64cbfeef-dfcd-4d3e-b75d-3ce08724a354" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_3560b3b2-6d33-4f35-b2f0-d17125e72569" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityRegistrantName_3560b3b2-6d33-4f35-b2f0-d17125e72569" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_5c617713-47b1-45fa-90cb-d9cded706574" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityIncorporationStateCountryCode_5c617713-47b1-45fa-90cb-d9cded706574" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_20975130-d44d-403e-8139-599d31a0436f" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityTaxIdentificationNumber_20975130-d44d-403e-8139-599d31a0436f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_bee5defc-c5f3-4bb9-a310-8f60d1a42e68" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityAddressAddressLine1_bee5defc-c5f3-4bb9-a310-8f60d1a42e68" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_36443037-d6be-4847-8472-c4fff6afe482" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityAddressCityOrTown_36443037-d6be-4847-8472-c4fff6afe482" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_d56082dc-002d-44fd-9f55-219dd4a1329b" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityAddressStateOrProvince_d56082dc-002d-44fd-9f55-219dd4a1329b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_e8d15a0c-4806-4a25-abae-24a62af636f5" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityAddressPostalZipCode_e8d15a0c-4806-4a25-abae-24a62af636f5" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_d46674eb-bcb8-4af4-ac8e-bf17fcb025be" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_CityAreaCode_d46674eb-bcb8-4af4-ac8e-bf17fcb025be" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_a74091af-2ff1-40a2-aa8c-cd00a7c1f5f1" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_LocalPhoneNumber_a74091af-2ff1-40a2-aa8c-cd00a7c1f5f1" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_4d0dbfda-e49d-4f42-acf1-ec247c7c1496" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_Security12bTitle_4d0dbfda-e49d-4f42-acf1-ec247c7c1496" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_4a034a2c-a452-489b-84a4-104788c040dd" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_TradingSymbol_4a034a2c-a452-489b-84a4-104788c040dd" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_9fbf3c62-b65f-492e-a157-7014b1b858f2" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_SecurityExchangeName_9fbf3c62-b65f-492e-a157-7014b1b858f2" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_e32b7049-64b5-4a58-8461-793fa31a20dd" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityCurrentReportingStatus_e32b7049-64b5-4a58-8461-793fa31a20dd" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_e73b110e-9392-4a65-9eac-8be25b577812" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityInteractiveDataCurrent_e73b110e-9392-4a65-9eac-8be25b577812" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_90ed85c3-bf2a-430c-badd-c18db405e02f" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityFilerCategory_90ed85c3-bf2a-430c-badd-c18db405e02f" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_3b60eb45-3900-4194-aeb1-70b1c834e1b2" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntitySmallBusiness_3b60eb45-3900-4194-aeb1-70b1c834e1b2" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_335d6da6-5423-4385-834c-b0eb96093a8c" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityEmergingGrowthCompany_335d6da6-5423-4385-834c-b0eb96093a8c" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_60430a40-82ef-48fc-ae98-0cb3c6bb424d" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityShellCompany_60430a40-82ef-48fc-ae98-0cb3c6bb424d" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_f5aefecb-ada9-42e2-abff-b3e401399e2e" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_f5aefecb-ada9-42e2-abff-b3e401399e2e" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_5bedffcc-356b-40ba-b55c-9d49a1301ec5" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_EntityCentralIndexKey_5bedffcc-356b-40ba-b55c-9d49a1301ec5" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_538f6677-fa9c-4a45-8cff-a48142374fa0" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_DocumentFiscalYearFocus_538f6677-fa9c-4a45-8cff-a48142374fa0" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_fa7dc70d-80e5-48ac-b3ce-5dc311d542c4" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_DocumentFiscalPeriodFocus_fa7dc70d-80e5-48ac-b3ce-5dc311d542c4" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_ceedcd6a-33e5-4844-b6a5-45e295c0d5aa" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_AmendmentFlag_ceedcd6a-33e5-4844-b6a5-45e295c0d5aa" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_NoTradingSymbolFlag_5854ba9f-0b5a-49ba-b600-01b16030d923" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_NoTradingSymbolFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_NoTradingSymbolFlag_5854ba9f-0b5a-49ba-b600-01b16030d923" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_57ab19b2-501a-4620-b036-8219d3c38786" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_3ee67c4a-d88e-491f-a1e5-9e31a5adb60c" xlink:to="loc_dei_CurrentFiscalYearEndDate_57ab19b2-501a-4620-b036-8219d3c38786" xlink:type="arc" order="29"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFEQUITY" xlink:type="simple" xlink:href="swx-20250331.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFEQUITY"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_e8ff0fe0-daf3-4a2d-94a2-86573f484d13" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_55b7929b-2ecb-4a88-b100-a3c89feef9c1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_e8ff0fe0-daf3-4a2d-94a2-86573f484d13" xlink:to="loc_us-gaap_StatementTable_55b7929b-2ecb-4a88-b100-a3c89feef9c1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_410a6a45-35e9-4fa8-bd28-c995b7e3bc57" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_55b7929b-2ecb-4a88-b100-a3c89feef9c1" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_410a6a45-35e9-4fa8-bd28-c995b7e3bc57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_410a6a45-35e9-4fa8-bd28-c995b7e3bc57_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_410a6a45-35e9-4fa8-bd28-c995b7e3bc57" xlink:to="loc_us-gaap_EquityComponentDomain_410a6a45-35e9-4fa8-bd28-c995b7e3bc57_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_50f667ff-7e72-40d4-93de-c102b65bc52d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_410a6a45-35e9-4fa8-bd28-c995b7e3bc57" xlink:to="loc_us-gaap_EquityComponentDomain_50f667ff-7e72-40d4-93de-c102b65bc52d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParentMember_9f508ea0-d8cb-4aa8-9c84-3034cca1fbcf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_50f667ff-7e72-40d4-93de-c102b65bc52d" xlink:to="loc_us-gaap_ParentMember_9f508ea0-d8cb-4aa8-9c84-3034cca1fbcf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_e9ccd3be-f3c4-4aca-ac0a-575c110b7440" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_9f508ea0-d8cb-4aa8-9c84-3034cca1fbcf" xlink:to="loc_us-gaap_CommonStockMember_e9ccd3be-f3c4-4aca-ac0a-575c110b7440" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_8ba8c67c-f1c2-4cc9-a0aa-0a24d7a66f78" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_9f508ea0-d8cb-4aa8-9c84-3034cca1fbcf" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_8ba8c67c-f1c2-4cc9-a0aa-0a24d7a66f78" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_451b8571-5b5a-4a19-98b0-cfee7221134d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_9f508ea0-d8cb-4aa8-9c84-3034cca1fbcf" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_451b8571-5b5a-4a19-98b0-cfee7221134d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_09bdc780-3c63-4f65-9107-e925e76a9a91" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_9f508ea0-d8cb-4aa8-9c84-3034cca1fbcf" xlink:to="loc_us-gaap_RetainedEarningsMember_09bdc780-3c63-4f65-9107-e925e76a9a91" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_aa403ea4-f798-4a4c-8721-cb01cd5906cd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_50f667ff-7e72-40d4-93de-c102b65bc52d" xlink:to="loc_us-gaap_NoncontrollingInterestMember_aa403ea4-f798-4a4c-8721-cb01cd5906cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c226b8f6-5e5a-4eec-996c-d93dec1a27cb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e8ff0fe0-daf3-4a2d-94a2-86573f484d13" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c226b8f6-5e5a-4eec-996c-d93dec1a27cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_763f2dc4-1bb3-4798-a05f-0dc308a8120d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c226b8f6-5e5a-4eec-996c-d93dec1a27cb" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_763f2dc4-1bb3-4798-a05f-0dc308a8120d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_b0a08773-77ed-4a28-818c-826d006f0490" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c226b8f6-5e5a-4eec-996c-d93dec1a27cb" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_b0a08773-77ed-4a28-818c-826d006f0490" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest_dea096c9-7461-4092-b292-f5efe893bf59" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c226b8f6-5e5a-4eec-996c-d93dec1a27cb" xlink:to="loc_us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest_dea096c9-7461-4092-b292-f5efe893bf59" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_ca8949a0-5f8d-467e-b37b-0130d0516928" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c226b8f6-5e5a-4eec-996c-d93dec1a27cb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_ca8949a0-5f8d-467e-b37b-0130d0516928" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_d7ce9066-e13a-4026-be22-d0de207095b7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c226b8f6-5e5a-4eec-996c-d93dec1a27cb" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_d7ce9066-e13a-4026-be22-d0de207095b7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStock_486b7661-0b70-4812-acad-b3a4fa45255c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c226b8f6-5e5a-4eec-996c-d93dec1a27cb" xlink:to="loc_us-gaap_DividendsCommonStock_486b7661-0b70-4812-acad-b3a4fa45255c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AdjustmentsToAdditionalPaidInCapitalPromissoryNotesInAssociationWithRedeemableNoncontrollingInterest_01eee020-ea76-4b62-8b27-354ec67c6586" xlink:href="swx-20250331.xsd#swx_AdjustmentsToAdditionalPaidInCapitalPromissoryNotesInAssociationWithRedeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c226b8f6-5e5a-4eec-996c-d93dec1a27cb" xlink:to="loc_swx_AdjustmentsToAdditionalPaidInCapitalPromissoryNotesInAssociationWithRedeemableNoncontrollingInterest_01eee020-ea76-4b62-8b27-354ec67c6586" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentBeforeTaxPortionAttributableToParent_400e016c-bf0f-4c9f-a757-6737d7038dd5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentBeforeTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c226b8f6-5e5a-4eec-996c-d93dec1a27cb" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentBeforeTaxPortionAttributableToParent_400e016c-bf0f-4c9f-a757-6737d7038dd5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTaxOther_3f66e0d1-1304-4433-905a-5984b277fb1d" xlink:href="swx-20250331.xsd#swx_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTaxOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c226b8f6-5e5a-4eec-996c-d93dec1a27cb" xlink:to="loc_swx_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTaxOther_3f66e0d1-1304-4433-905a-5984b277fb1d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestChangeInRedemptionValue_b8fcb92f-49b0-4f25-af8d-5cf592c2bba5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MinorityInterestChangeInRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_c226b8f6-5e5a-4eec-996c-d93dec1a27cb" xlink:to="loc_us-gaap_MinorityInterestChangeInRedemptionValue_b8fcb92f-49b0-4f25-af8d-5cf592c2bba5" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_a087acc7-93a7-46e2-8d3d-40def0f20dc0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_c8a9bb02-e213-4fd1-ae7e-53c5d5b0660b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSSouthwest" xlink:type="simple" xlink:href="swx-20250331.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSSouthwest"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSSouthwest" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_df9e1a35-0a69-4a90-9cb2-e499d1ac5ef7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_cd2c936a-2fc7-4605-a970-d8f5e2efaf56" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_df9e1a35-0a69-4a90-9cb2-e499d1ac5ef7" xlink:to="loc_us-gaap_StatementTable_cd2c936a-2fc7-4605-a970-d8f5e2efaf56" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_1191a504-b534-4f0a-a4ac-fce1493931bc" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_cd2c936a-2fc7-4605-a970-d8f5e2efaf56" xlink:to="loc_dei_LegalEntityAxis_1191a504-b534-4f0a-a4ac-fce1493931bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_1191a504-b534-4f0a-a4ac-fce1493931bc_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1191a504-b534-4f0a-a4ac-fce1493931bc" xlink:to="loc_dei_EntityDomain_1191a504-b534-4f0a-a4ac-fce1493931bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_9d8a2936-540b-429d-bda7-017319119a2d" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1191a504-b534-4f0a-a4ac-fce1493931bc" xlink:to="loc_dei_EntityDomain_9d8a2936-540b-429d-bda7-017319119a2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_27888194-43b2-4d02-9163-e9a46f67f8fc" xlink:href="swx-20250331.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_9d8a2936-540b-429d-bda7-017319119a2d" xlink:to="loc_swx_SouthwestGasCorporationMember_27888194-43b2-4d02-9163-e9a46f67f8fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_a8c315d1-43db-46ad-af44-6f6243a1686d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_cd2c936a-2fc7-4605-a970-d8f5e2efaf56" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_a8c315d1-43db-46ad-af44-6f6243a1686d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_a8c315d1-43db-46ad-af44-6f6243a1686d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_a8c315d1-43db-46ad-af44-6f6243a1686d" xlink:to="loc_us-gaap_RelatedPartyDomain_a8c315d1-43db-46ad-af44-6f6243a1686d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_60dc3e95-ba02-4439-92d1-48ecb0bcd2c1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_a8c315d1-43db-46ad-af44-6f6243a1686d" xlink:to="loc_us-gaap_RelatedPartyDomain_60dc3e95-ba02-4439-92d1-48ecb0bcd2c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_903bc57b-2507-4e0a-b0a7-03a8e95acef4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_60dc3e95-ba02-4439-92d1-48ecb0bcd2c1" xlink:to="loc_us-gaap_RelatedPartyMember_903bc57b-2507-4e0a-b0a7-03a8e95acef4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonrelatedPartyMember_2360b83a-5f0a-49ae-812d-3c047fac3772" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NonrelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_60dc3e95-ba02-4439-92d1-48ecb0bcd2c1" xlink:to="loc_us-gaap_NonrelatedPartyMember_2360b83a-5f0a-49ae-812d-3c047fac3772" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_aea84cbd-01f8-4659-b902-bc188f795f0f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_df9e1a35-0a69-4a90-9cb2-e499d1ac5ef7" xlink:to="loc_us-gaap_AssetsAbstract_aea84cbd-01f8-4659-b902-bc188f795f0f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract_fb0c8849-6305-4d9c-a622-b815933ddc2b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_aea84cbd-01f8-4659-b902-bc188f795f0f" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract_fb0c8849-6305-4d9c-a622-b815933ddc2b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_PublicUtilitiesPropertyPlantandEquipmentGasPlant_59e4cfe9-cc6e-4c2c-a181-4ca152dc446b" xlink:href="swx-20250331.xsd#swx_PublicUtilitiesPropertyPlantandEquipmentGasPlant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract_fb0c8849-6305-4d9c-a622-b815933ddc2b" xlink:to="loc_swx_PublicUtilitiesPropertyPlantandEquipmentGasPlant_59e4cfe9-cc6e-4c2c-a181-4ca152dc446b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation_5ef9992d-16d1-479e-9e36-8ac77e63c8a2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract_fb0c8849-6305-4d9c-a622-b815933ddc2b" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation_5ef9992d-16d1-479e-9e36-8ac77e63c8a2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress_5bdb8c50-30b7-4212-8b13-06c13119bdf6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract_fb0c8849-6305-4d9c-a622-b815933ddc2b" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress_5bdb8c50-30b7-4212-8b13-06c13119bdf6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet_893ecebb-a2a4-4075-8ebc-40bc109efcf4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract_fb0c8849-6305-4d9c-a622-b815933ddc2b" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet_893ecebb-a2a4-4075-8ebc-40bc109efcf4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OtherPropertyAndInvestments_144ebced-41c9-44ed-acaf-a4a93d839433" xlink:href="swx-20250331.xsd#swx_OtherPropertyAndInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_aea84cbd-01f8-4659-b902-bc188f795f0f" xlink:to="loc_swx_OtherPropertyAndInvestments_144ebced-41c9-44ed-acaf-a4a93d839433" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_b77e9bc3-a995-42f8-9bef-f905d0209b6d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_aea84cbd-01f8-4659-b902-bc188f795f0f" xlink:to="loc_us-gaap_AssetsCurrentAbstract_b77e9bc3-a995-42f8-9bef-f905d0209b6d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_9aa87bb1-27fc-4b16-9a53-678cc1fa25ad" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_b77e9bc3-a995-42f8-9bef-f905d0209b6d" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_9aa87bb1-27fc-4b16-9a53-678cc1fa25ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_b3ccf856-bc48-453b-881e-904647dc99dc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_b77e9bc3-a995-42f8-9bef-f905d0209b6d" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_b3ccf856-bc48-453b-881e-904647dc99dc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccruedUtilityRevenue_5d8e9b48-0703-4979-980f-5fba305e069d" xlink:href="swx-20250331.xsd#swx_AccruedUtilityRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_b77e9bc3-a995-42f8-9bef-f905d0209b6d" xlink:to="loc_swx_AccruedUtilityRevenue_5d8e9b48-0703-4979-980f-5fba305e069d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredGasCost_94c4fb61-4d67-42cf-ab0b-de0280274cb5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredGasCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_b77e9bc3-a995-42f8-9bef-f905d0209b6d" xlink:to="loc_us-gaap_DeferredGasCost_94c4fb61-4d67-42cf-ab0b-de0280274cb5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_a30e77c7-a6e3-47d9-bd29-44abb7547db8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_b77e9bc3-a995-42f8-9bef-f905d0209b6d" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_a30e77c7-a6e3-47d9-bd29-44abb7547db8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_b53cad5b-902d-48fd-8408-4916702515f4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_b77e9bc3-a995-42f8-9bef-f905d0209b6d" xlink:to="loc_us-gaap_AssetsCurrent_b53cad5b-902d-48fd-8408-4916702515f4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrentAbstract_58adc77a-5275-4eb4-a16f-8d66333d1b79" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_aea84cbd-01f8-4659-b902-bc188f795f0f" xlink:to="loc_us-gaap_AssetsNoncurrentAbstract_58adc77a-5275-4eb4-a16f-8d66333d1b79" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_6c2c3931-fcf6-4dc6-8ae9-7a1339f53b08" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_58adc77a-5275-4eb4-a16f-8d66333d1b79" xlink:to="loc_us-gaap_Goodwill_6c2c3931-fcf6-4dc6-8ae9-7a1339f53b08" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_78ed01b4-2305-4937-8bf2-6151af0428e1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_58adc77a-5275-4eb4-a16f-8d66333d1b79" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_78ed01b4-2305-4937-8bf2-6151af0428e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrentOtherThanNoncurrentInvestmentsAndPropertyPlantAndEquipment_861fbb0f-c6a5-44bc-aa35-ace29ce86da0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsNoncurrentOtherThanNoncurrentInvestmentsAndPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_58adc77a-5275-4eb4-a16f-8d66333d1b79" xlink:to="loc_us-gaap_AssetsNoncurrentOtherThanNoncurrentInvestmentsAndPropertyPlantAndEquipment_861fbb0f-c6a5-44bc-aa35-ace29ce86da0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_917727e7-02b1-4a31-b0d0-0df23aea095a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_aea84cbd-01f8-4659-b902-bc188f795f0f" xlink:to="loc_us-gaap_Assets_917727e7-02b1-4a31-b0d0-0df23aea095a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_e806ab52-2e86-459c-830d-3395fe719c71" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_df9e1a35-0a69-4a90-9cb2-e499d1ac5ef7" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_e806ab52-2e86-459c-830d-3395fe719c71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_2494b92c-e2d9-4b22-b955-3782e10019aa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CapitalizationLongtermDebtAndEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_e806ab52-2e86-459c-830d-3395fe719c71" xlink:to="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_2494b92c-e2d9-4b22-b955-3782e10019aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_b036c836-31ec-4a7a-b248-76545cc0105b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_2494b92c-e2d9-4b22-b955-3782e10019aa" xlink:to="loc_us-gaap_CommonStockValue_b036c836-31ec-4a7a-b248-76545cc0105b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_95676394-9ff7-4bb6-8027-0d51fac98d01" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_2494b92c-e2d9-4b22-b955-3782e10019aa" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_95676394-9ff7-4bb6-8027-0d51fac98d01" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_7d665691-6548-4d78-aacd-07b41b4a7662" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_2494b92c-e2d9-4b22-b955-3782e10019aa" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_7d665691-6548-4d78-aacd-07b41b4a7662" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_481f3173-756b-4992-a75b-410bafb59286" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_2494b92c-e2d9-4b22-b955-3782e10019aa" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_481f3173-756b-4992-a75b-410bafb59286" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_792e38b1-54cd-4bbf-99cc-f0fdea420dc6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_2494b92c-e2d9-4b22-b955-3782e10019aa" xlink:to="loc_us-gaap_StockholdersEquity_792e38b1-54cd-4bbf-99cc-f0fdea420dc6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_98e1462f-9601-4afa-a07f-857c363cf05d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_2494b92c-e2d9-4b22-b955-3782e10019aa" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_98e1462f-9601-4afa-a07f-857c363cf05d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizationLongtermDebtAndEquity_03c745ec-5ebc-475e-bfce-09b0d910db73" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CapitalizationLongtermDebtAndEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_2494b92c-e2d9-4b22-b955-3782e10019aa" xlink:to="loc_us-gaap_CapitalizationLongtermDebtAndEquity_03c745ec-5ebc-475e-bfce-09b0d910db73" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_d9bb46e2-00b6-40e6-91c7-dd495c99bbd6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_e806ab52-2e86-459c-830d-3395fe719c71" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_d9bb46e2-00b6-40e6-91c7-dd495c99bbd6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_32a685fb-6755-483f-838e-39a53dd0a1ac" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d9bb46e2-00b6-40e6-91c7-dd495c99bbd6" xlink:to="loc_us-gaap_AccountsPayableCurrent_32a685fb-6755-483f-838e-39a53dd0a1ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_e3f8d67b-6c56-43de-bb69-012389120772" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d9bb46e2-00b6-40e6-91c7-dd495c99bbd6" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_e3f8d67b-6c56-43de-bb69-012389120772" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxesCurrent_1b57c440-5de0-4991-93d7-370d784bdc52" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccruedIncomeTaxesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d9bb46e2-00b6-40e6-91c7-dd495c99bbd6" xlink:to="loc_us-gaap_AccruedIncomeTaxesCurrent_1b57c440-5de0-4991-93d7-370d784bdc52" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent_052452b1-6a6e-4736-bbe7-59545babc940" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d9bb46e2-00b6-40e6-91c7-dd495c99bbd6" xlink:to="loc_us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent_052452b1-6a6e-4736-bbe7-59545babc940" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrent_19a83f7a-fdb0-421c-9cab-ec106ef8c392" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d9bb46e2-00b6-40e6-91c7-dd495c99bbd6" xlink:to="loc_us-gaap_InterestPayableCurrent_19a83f7a-fdb0-421c-9cab-ec106ef8c392" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredGasPurchasesCurrent_9d5c813d-0366-43ee-aca5-d29ec39e5926" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredGasPurchasesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d9bb46e2-00b6-40e6-91c7-dd495c99bbd6" xlink:to="loc_us-gaap_DeferredGasPurchasesCurrent_9d5c813d-0366-43ee-aca5-d29ec39e5926" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_7b82c8db-83fc-4a94-b45d-3bd6e3023af9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d9bb46e2-00b6-40e6-91c7-dd495c99bbd6" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_7b82c8db-83fc-4a94-b45d-3bd6e3023af9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_1d3aa6b4-ced5-4d27-9d51-71d09ab1c6d7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_d9bb46e2-00b6-40e6-91c7-dd495c99bbd6" xlink:to="loc_us-gaap_LiabilitiesCurrent_1d3aa6b4-ced5-4d27-9d51-71d09ab1c6d7" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_fe2b7f8c-8027-4c28-94bd-21a8b179e709" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherLiabilitiesNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_e806ab52-2e86-459c-830d-3395fe719c71" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_fe2b7f8c-8027-4c28-94bd-21a8b179e709" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DeferredIncomeTaxesAndUnamortizedInvestmentTaxCredits_71f56dee-6dd7-489d-9328-215e6fc3c4aa" xlink:href="swx-20250331.xsd#swx_DeferredIncomeTaxesAndUnamortizedInvestmentTaxCredits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_fe2b7f8c-8027-4c28-94bd-21a8b179e709" xlink:to="loc_swx_DeferredIncomeTaxesAndUnamortizedInvestmentTaxCredits_71f56dee-6dd7-489d-9328-215e6fc3c4aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesNoncurrent_b711524e-1f82-4404-a089-cb7acb74dc28" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherAccruedLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_fe2b7f8c-8027-4c28-94bd-21a8b179e709" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesNoncurrent_b711524e-1f82-4404-a089-cb7acb74dc28" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCreditsAndOtherLiabilitiesNoncurrent_bd409095-3560-4a6f-a165-b863c748f22f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredCreditsAndOtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_fe2b7f8c-8027-4c28-94bd-21a8b179e709" xlink:to="loc_us-gaap_DeferredCreditsAndOtherLiabilitiesNoncurrent_bd409095-3560-4a6f-a165-b863c748f22f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_bb414ca5-f744-4226-a8a2-2e05f5bf9c6b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_fe2b7f8c-8027-4c28-94bd-21a8b179e709" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_bb414ca5-f744-4226-a8a2-2e05f5bf9c6b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_b0246661-b3e0-4954-9345-8e366d80b9be" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_e806ab52-2e86-459c-830d-3395fe719c71" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_b0246661-b3e0-4954-9345-8e366d80b9be" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFINCOMESouthwest" xlink:type="simple" xlink:href="swx-20250331.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFINCOMESouthwest"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFINCOMESouthwest" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_79816181-799c-4e17-bf2a-15b8a74c845e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_cfb44dbb-7f1a-48b4-a593-416768a4fe28" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_79816181-799c-4e17-bf2a-15b8a74c845e" xlink:to="loc_us-gaap_StatementTable_cfb44dbb-7f1a-48b4-a593-416768a4fe28" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_198e90be-fec7-485f-8975-03e5cb624d64" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_cfb44dbb-7f1a-48b4-a593-416768a4fe28" xlink:to="loc_dei_LegalEntityAxis_198e90be-fec7-485f-8975-03e5cb624d64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_198e90be-fec7-485f-8975-03e5cb624d64_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_198e90be-fec7-485f-8975-03e5cb624d64" xlink:to="loc_dei_EntityDomain_198e90be-fec7-485f-8975-03e5cb624d64_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_344e45f5-ecbe-4329-b97a-c5e02e378705" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_198e90be-fec7-485f-8975-03e5cb624d64" xlink:to="loc_dei_EntityDomain_344e45f5-ecbe-4329-b97a-c5e02e378705" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_ca47cc5f-a5b7-4db1-88f9-e7aa11b7f77e" xlink:href="swx-20250331.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_344e45f5-ecbe-4329-b97a-c5e02e378705" xlink:to="loc_swx_SouthwestGasCorporationMember_ca47cc5f-a5b7-4db1-88f9-e7aa11b7f77e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatedAndUnregulatedOperatingRevenue_df60fa87-88f4-4559-bcd1-1991ebd410a0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RegulatedAndUnregulatedOperatingRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_79816181-799c-4e17-bf2a-15b8a74c845e" xlink:to="loc_us-gaap_RegulatedAndUnregulatedOperatingRevenue_df60fa87-88f4-4559-bcd1-1991ebd410a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_e9da2b42-407b-4549-88d3-883256e56965" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_79816181-799c-4e17-bf2a-15b8a74c845e" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_e9da2b42-407b-4549-88d3-883256e56965" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseGasAndPetroleumPurchased_cd3af154-229e-4114-9a04-940de6cae886" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UtilitiesOperatingExpenseGasAndPetroleumPurchased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_e9da2b42-407b-4549-88d3-883256e56965" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseGasAndPetroleumPurchased_cd3af154-229e-4114-9a04-940de6cae886" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_67031bbb-e51c-498f-b83b-83556d02536d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_e9da2b42-407b-4549-88d3-883256e56965" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_67031bbb-e51c-498f-b83b-83556d02536d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_b600635c-bec2-4de9-b430-4260bd0971dc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_e9da2b42-407b-4549-88d3-883256e56965" xlink:to="loc_us-gaap_DepreciationAndAmortization_b600635c-bec2-4de9-b430-4260bd0971dc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_f35a7d73-e5c8-46f4-a563-d46696fca0d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TaxesExcludingIncomeAndExciseTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_e9da2b42-407b-4549-88d3-883256e56965" xlink:to="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_f35a7d73-e5c8-46f4-a563-d46696fca0d6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_bfcad37b-569d-4473-a09f-dc4ead70fb50" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_e9da2b42-407b-4549-88d3-883256e56965" xlink:to="loc_us-gaap_CostsAndExpenses_bfcad37b-569d-4473-a09f-dc4ead70fb50" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_00c743ee-a53b-4d96-8e2a-bdded820f30a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_79816181-799c-4e17-bf2a-15b8a74c845e" xlink:to="loc_us-gaap_OperatingIncomeLoss_00c743ee-a53b-4d96-8e2a-bdded820f30a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpenseAbstract_4c95a3a6-4894-4453-b5b7-3d873dd015e3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_79816181-799c-4e17-bf2a-15b8a74c845e" xlink:to="loc_us-gaap_NonoperatingIncomeExpenseAbstract_4c95a3a6-4894-4453-b5b7-3d873dd015e3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_2e69f968-2a9a-4736-a5c9-8c7734313a8d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_4c95a3a6-4894-4453-b5b7-3d873dd015e3" xlink:to="loc_us-gaap_InterestExpenseNonoperating_2e69f968-2a9a-4736-a5c9-8c7734313a8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_5975284b-f3f7-4415-804b-191f656ed114" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_4c95a3a6-4894-4453-b5b7-3d873dd015e3" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_5975284b-f3f7-4415-804b-191f656ed114" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_66474626-17b9-4bb6-bce4-47f3fb518497" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_4c95a3a6-4894-4453-b5b7-3d873dd015e3" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_66474626-17b9-4bb6-bce4-47f3fb518497" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_0033b9ac-6a34-4298-97fe-c1cbb18ee82a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_79816181-799c-4e17-bf2a-15b8a74c845e" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_0033b9ac-6a34-4298-97fe-c1cbb18ee82a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_add57fb9-3a3e-47a4-a257-f9e7d6f328d0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_79816181-799c-4e17-bf2a-15b8a74c845e" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_add57fb9-3a3e-47a4-a257-f9e7d6f328d0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_7c5bf66f-972a-4f24-8d59-9c877485a248" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_79816181-799c-4e17-bf2a-15b8a74c845e" xlink:to="loc_us-gaap_NetIncomeLoss_7c5bf66f-972a-4f24-8d59-9c877485a248" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMESouthwest" xlink:type="simple" xlink:href="swx-20250331.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMESouthwest"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMESouthwest" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_14219b47-d24e-496a-8035-8b7b0f187907" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_e50c8451-f301-49cf-a2bd-0a8830fb8841" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_14219b47-d24e-496a-8035-8b7b0f187907" xlink:to="loc_us-gaap_StatementTable_e50c8451-f301-49cf-a2bd-0a8830fb8841" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_f2db4c5f-cfe8-4429-9444-ecaeee284245" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_e50c8451-f301-49cf-a2bd-0a8830fb8841" xlink:to="loc_dei_LegalEntityAxis_f2db4c5f-cfe8-4429-9444-ecaeee284245" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_f2db4c5f-cfe8-4429-9444-ecaeee284245_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_f2db4c5f-cfe8-4429-9444-ecaeee284245" xlink:to="loc_dei_EntityDomain_f2db4c5f-cfe8-4429-9444-ecaeee284245_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_c12a0c87-0bc2-4544-a967-7a6b79162adc" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_f2db4c5f-cfe8-4429-9444-ecaeee284245" xlink:to="loc_dei_EntityDomain_c12a0c87-0bc2-4544-a967-7a6b79162adc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_68810699-6a88-485c-ad86-3e0c8be23314" xlink:href="swx-20250331.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_c12a0c87-0bc2-4544-a967-7a6b79162adc" xlink:to="loc_swx_SouthwestGasCorporationMember_68810699-6a88-485c-ad86-3e0c8be23314" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_d67d67db-0c88-4c1e-8102-921a85a64463" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_14219b47-d24e-496a-8035-8b7b0f187907" xlink:to="loc_us-gaap_ProfitLoss_d67d67db-0c88-4c1e-8102-921a85a64463" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_0ddb66f0-2916-47f3-95b0-47654e82b5e9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_14219b47-d24e-496a-8035-8b7b0f187907" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_0ddb66f0-2916-47f3-95b0-47654e82b5e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_f3ddfb46-a988-489c-82f3-32b023477afe" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_0ddb66f0-2916-47f3-95b0-47654e82b5e9" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_f3ddfb46-a988-489c-82f3-32b023477afe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax_3f41c380-da16-44fa-833d-2e57cda78517" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_f3ddfb46-a988-489c-82f3-32b023477afe" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax_3f41c380-da16-44fa-833d-2e57cda78517" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax_bdf49beb-128c-4fbe-8040-064d52fe3928" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_f3ddfb46-a988-489c-82f3-32b023477afe" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax_bdf49beb-128c-4fbe-8040-064d52fe3928" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OtherComprehensiveIncomeDefinedBenefitPlansRegulatoryAdjustmentNetOfTax_fcfccd63-8a7b-4328-b924-626a896ce782" xlink:href="swx-20250331.xsd#swx_OtherComprehensiveIncomeDefinedBenefitPlansRegulatoryAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_f3ddfb46-a988-489c-82f3-32b023477afe" xlink:to="loc_swx_OtherComprehensiveIncomeDefinedBenefitPlansRegulatoryAdjustmentNetOfTax_fcfccd63-8a7b-4328-b924-626a896ce782" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_6b8dd7cf-ac05-4e60-9127-a56def243dff" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_f3ddfb46-a988-489c-82f3-32b023477afe" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_6b8dd7cf-ac05-4e60-9127-a56def243dff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_1d2fec94-f41b-477a-8022-17de5e24cd3d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_14219b47-d24e-496a-8035-8b7b0f187907" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_1d2fec94-f41b-477a-8022-17de5e24cd3d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_09c5d0dd-8062-4087-9235-1ba67897f0a9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_14219b47-d24e-496a-8035-8b7b0f187907" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_09c5d0dd-8062-4087-9235-1ba67897f0a9" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSSouthwest" xlink:type="simple" xlink:href="swx-20250331.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSSouthwest"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSSouthwest" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_b62b706d-ebca-4b2c-8805-3f8f783d2564" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_1875c05c-3863-432e-85cb-7e7effc44300" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_b62b706d-ebca-4b2c-8805-3f8f783d2564" xlink:to="loc_us-gaap_StatementTable_1875c05c-3863-432e-85cb-7e7effc44300" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_b7587700-61af-4dbe-be76-3ca14dfd2918" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_1875c05c-3863-432e-85cb-7e7effc44300" xlink:to="loc_dei_LegalEntityAxis_b7587700-61af-4dbe-be76-3ca14dfd2918" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_b7587700-61af-4dbe-be76-3ca14dfd2918_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_b7587700-61af-4dbe-be76-3ca14dfd2918" xlink:to="loc_dei_EntityDomain_b7587700-61af-4dbe-be76-3ca14dfd2918_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_397c7747-728e-42b5-8b3b-a6842922ddaf" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_b7587700-61af-4dbe-be76-3ca14dfd2918" xlink:to="loc_dei_EntityDomain_397c7747-728e-42b5-8b3b-a6842922ddaf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_e7234e76-26e1-4e30-8f7d-a56b2dd01128" xlink:href="swx-20250331.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_397c7747-728e-42b5-8b3b-a6842922ddaf" xlink:to="loc_swx_SouthwestGasCorporationMember_e7234e76-26e1-4e30-8f7d-a56b2dd01128" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_9298f729-d486-4805-a573-e606308348bb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b62b706d-ebca-4b2c-8805-3f8f783d2564" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_9298f729-d486-4805-a573-e606308348bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_ab7a7184-cb8b-4d82-bb2d-c4a4feb6e7f2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_9298f729-d486-4805-a573-e606308348bb" xlink:to="loc_us-gaap_ProfitLoss_ab7a7184-cb8b-4d82-bb2d-c4a4feb6e7f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_a1074417-aa52-4241-af2c-9c11f08ff4ee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_9298f729-d486-4805-a573-e606308348bb" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_a1074417-aa52-4241-af2c-9c11f08ff4ee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_89f507c5-acaa-4dc4-86ba-3edf5ca846ed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_a1074417-aa52-4241-af2c-9c11f08ff4ee" xlink:to="loc_us-gaap_DepreciationAndAmortization_89f507c5-acaa-4dc4-86ba-3edf5ca846ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredIncomeTaxes_218a0e91-84e4-4f00-ba0b-3ea30d4f0bd0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInDeferredIncomeTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_a1074417-aa52-4241-af2c-9c11f08ff4ee" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredIncomeTaxes_218a0e91-84e4-4f00-ba0b-3ea30d4f0bd0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_ae34bd0e-b387-43e1-94d9-3b5c338f7d5e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_a1074417-aa52-4241-af2c-9c11f08ff4ee" xlink:to="loc_us-gaap_ShareBasedCompensation_ae34bd0e-b387-43e1-94d9-3b5c338f7d5e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction_bc96ebea-8974-4308-873d-7ee37dcba95c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_a1074417-aa52-4241-af2c-9c11f08ff4ee" xlink:to="loc_us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction_bc96ebea-8974-4308-873d-7ee37dcba95c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_0efdd459-96a7-43d3-9aed-e803d333cc00" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_a1074417-aa52-4241-af2c-9c11f08ff4ee" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_0efdd459-96a7-43d3-9aed-e803d333cc00" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_386b1daf-110f-4254-9f13-43275745830f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_0efdd459-96a7-43d3-9aed-e803d333cc00" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_386b1daf-110f-4254-9f13-43275745830f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_IncreaseDecreaseInAccruedUtilityRevenue_d316ad24-d928-4cdb-9f7a-265f9d05e4db" xlink:href="swx-20250331.xsd#swx_IncreaseDecreaseInAccruedUtilityRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_0efdd459-96a7-43d3-9aed-e803d333cc00" xlink:to="loc_swx_IncreaseDecreaseInAccruedUtilityRevenue_d316ad24-d928-4cdb-9f7a-265f9d05e4db" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredGasCost_664c6d7d-2eeb-4e1b-b719-03e0ba613429" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInDeferredGasCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_0efdd459-96a7-43d3-9aed-e803d333cc00" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredGasCost_664c6d7d-2eeb-4e1b-b719-03e0ba613429" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_1fd1ba51-0eeb-4bd1-a5dc-36dcccccc6d8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_0efdd459-96a7-43d3-9aed-e803d333cc00" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_1fd1ba51-0eeb-4bd1-a5dc-36dcccccc6d8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedTaxesPayable_a5376077-7b56-481a-8173-0f8736017942" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInAccruedTaxesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_0efdd459-96a7-43d3-9aed-e803d333cc00" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedTaxesPayable_a5376077-7b56-481a-8173-0f8736017942" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherCurrentAssetsAndLiabilitiesNet_da0ea828-c9ce-4f2d-acc7-a0b808c734a6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInOtherCurrentAssetsAndLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_0efdd459-96a7-43d3-9aed-e803d333cc00" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherCurrentAssetsAndLiabilitiesNet_da0ea828-c9ce-4f2d-acc7-a0b808c734a6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_701d0a4c-ae92-4644-9036-b9ca262eb2c0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_9298f729-d486-4805-a573-e606308348bb" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_701d0a4c-ae92-4644-9036-b9ca262eb2c0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_628b5cdd-cd1a-4c7d-89d7-8d555b79a8d7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInOtherOperatingLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_9298f729-d486-4805-a573-e606308348bb" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_628b5cdd-cd1a-4c7d-89d7-8d555b79a8d7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_295745f0-2254-40fe-97dd-c0936cbc91d5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_9298f729-d486-4805-a573-e606308348bb" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_295745f0-2254-40fe-97dd-c0936cbc91d5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_dd37c758-bb58-4161-b75f-0a8f9566cbec" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b62b706d-ebca-4b2c-8805-3f8f783d2564" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_dd37c758-bb58-4161-b75f-0a8f9566cbec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_bda7f1e4-d014-484f-96c6-e05169b6bada" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_dd37c758-bb58-4161-b75f-0a8f9566cbec" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_bda7f1e4-d014-484f-96c6-e05169b6bada" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_281a2175-baf2-42b4-b447-37506f6f0139" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_dd37c758-bb58-4161-b75f-0a8f9566cbec" xlink:to="loc_us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_281a2175-baf2-42b4-b447-37506f6f0139" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_ChangesInCustomerAdvancesInvestingActivities_6b068fb6-01f6-4a38-9d3f-d27942995c68" xlink:href="swx-20250331.xsd#swx_ChangesInCustomerAdvancesInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_dd37c758-bb58-4161-b75f-0a8f9566cbec" xlink:to="loc_swx_ChangesInCustomerAdvancesInvestingActivities_6b068fb6-01f6-4a38-9d3f-d27942995c68" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_cc371167-d767-4667-8e45-913d045fe286" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsForProceedsFromOtherInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_dd37c758-bb58-4161-b75f-0a8f9566cbec" xlink:to="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_cc371167-d767-4667-8e45-913d045fe286" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_d517b6a1-b494-41ee-81fb-0aeaae97bb79" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_dd37c758-bb58-4161-b75f-0a8f9566cbec" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_d517b6a1-b494-41ee-81fb-0aeaae97bb79" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_71171fd4-d955-4d44-b403-99a96666ad68" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b62b706d-ebca-4b2c-8805-3f8f783d2564" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_71171fd4-d955-4d44-b403-99a96666ad68" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividendsCommonStock_7e8aaed6-d1ee-4085-b67a-3c7fddf5902a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsOfDividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_71171fd4-d955-4d44-b403-99a96666ad68" xlink:to="loc_us-gaap_PaymentsOfDividendsCommonStock_7e8aaed6-d1ee-4085-b67a-3c7fddf5902a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_31a7d591-bbce-402f-89f9-92db32b984e1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_71171fd4-d955-4d44-b403-99a96666ad68" xlink:to="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_31a7d591-bbce-402f-89f9-92db32b984e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_1f41bfca-94b0-456d-98a7-41c3657a499d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromPaymentsForOtherFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_71171fd4-d955-4d44-b403-99a96666ad68" xlink:to="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_1f41bfca-94b0-456d-98a7-41c3657a499d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_456cff70-8f92-4ba6-9a79-32e80c161094" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_71171fd4-d955-4d44-b403-99a96666ad68" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_456cff70-8f92-4ba6-9a79-32e80c161094" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_15fa337c-7fa5-45d7-92d7-51b04e787112" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b62b706d-ebca-4b2c-8805-3f8f783d2564" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_15fa337c-7fa5-45d7-92d7-51b04e787112" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_25f96dd0-724b-4ab0-90cf-771bb8e0b468" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b62b706d-ebca-4b2c-8805-3f8f783d2564" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_25f96dd0-724b-4ab0-90cf-771bb8e0b468" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_7ba03503-bf46-4566-a1bc-bd830c5a3bcb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_e6c981b6-6a88-4e75-a602-15109e6aac96" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplementalCashFlowInformationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b62b706d-ebca-4b2c-8805-3f8f783d2564" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_e6c981b6-6a88-4e75-a602-15109e6aac96" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaidNet_a496d11b-b74a-4070-b459-4f4796954e19" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_e6c981b6-6a88-4e75-a602-15109e6aac96" xlink:to="loc_us-gaap_InterestPaidNet_a496d11b-b74a-4070-b459-4f4796954e19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_8f0e9fe5-b75c-4ee6-b32a-4eafa8e166a8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxesPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_e6c981b6-6a88-4e75-a602-15109e6aac96" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_8f0e9fe5-b75c-4ee6-b32a-4eafa8e166a8" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFEQUITYSouthwest" xlink:type="simple" xlink:href="swx-20250331.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFEQUITYSouthwest"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFEQUITYSouthwest" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_220af3af-16c2-40df-876a-92400d5c3677" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_06a715be-c330-4a60-9656-ac527e99c53d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_220af3af-16c2-40df-876a-92400d5c3677" xlink:to="loc_us-gaap_StatementTable_06a715be-c330-4a60-9656-ac527e99c53d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_24fead26-cc61-43c8-b677-a48de216c9ac" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_06a715be-c330-4a60-9656-ac527e99c53d" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_24fead26-cc61-43c8-b677-a48de216c9ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_24fead26-cc61-43c8-b677-a48de216c9ac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_24fead26-cc61-43c8-b677-a48de216c9ac" xlink:to="loc_us-gaap_EquityComponentDomain_24fead26-cc61-43c8-b677-a48de216c9ac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_9c32489b-31ba-4e8e-8bfb-f2ad6773b4c6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_24fead26-cc61-43c8-b677-a48de216c9ac" xlink:to="loc_us-gaap_EquityComponentDomain_9c32489b-31ba-4e8e-8bfb-f2ad6773b4c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_70c0c84c-dfb7-4e6f-9ced-68bcdb7f2da9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_9c32489b-31ba-4e8e-8bfb-f2ad6773b4c6" xlink:to="loc_us-gaap_CommonStockMember_70c0c84c-dfb7-4e6f-9ced-68bcdb7f2da9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_50b1ab0f-2963-484e-913e-af4254ab97c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_9c32489b-31ba-4e8e-8bfb-f2ad6773b4c6" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_50b1ab0f-2963-484e-913e-af4254ab97c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_7b36b685-cb93-4aed-9664-528e99b195c0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_9c32489b-31ba-4e8e-8bfb-f2ad6773b4c6" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_7b36b685-cb93-4aed-9664-528e99b195c0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_72479e62-f43c-4e15-a0a1-fdddaf178ab2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_9c32489b-31ba-4e8e-8bfb-f2ad6773b4c6" xlink:to="loc_us-gaap_RetainedEarningsMember_72479e62-f43c-4e15-a0a1-fdddaf178ab2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParentMember_8270f461-1212-4c8a-aae1-6a7d1af90878" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_9c32489b-31ba-4e8e-8bfb-f2ad6773b4c6" xlink:to="loc_us-gaap_ParentMember_8270f461-1212-4c8a-aae1-6a7d1af90878" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_95a29093-51d8-4e30-bc2d-8cac0b500e08" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_06a715be-c330-4a60-9656-ac527e99c53d" xlink:to="loc_dei_LegalEntityAxis_95a29093-51d8-4e30-bc2d-8cac0b500e08" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_95a29093-51d8-4e30-bc2d-8cac0b500e08_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_95a29093-51d8-4e30-bc2d-8cac0b500e08" xlink:to="loc_dei_EntityDomain_95a29093-51d8-4e30-bc2d-8cac0b500e08_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_81a4ecfc-a354-4d03-812b-ce99092addaa" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_95a29093-51d8-4e30-bc2d-8cac0b500e08" xlink:to="loc_dei_EntityDomain_81a4ecfc-a354-4d03-812b-ce99092addaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_3ddb33df-ffca-4b64-9a50-14dee6eb6097" xlink:href="swx-20250331.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_81a4ecfc-a354-4d03-812b-ce99092addaa" xlink:to="loc_swx_SouthwestGasCorporationMember_3ddb33df-ffca-4b64-9a50-14dee6eb6097" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_cf70b0ba-37e3-46bd-9237-3c13f88fcfda" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_220af3af-16c2-40df-876a-92400d5c3677" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_cf70b0ba-37e3-46bd-9237-3c13f88fcfda" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_16299893-7c0c-41eb-a640-fc85b9803c96" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_cf70b0ba-37e3-46bd-9237-3c13f88fcfda" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_16299893-7c0c-41eb-a640-fc85b9803c96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_de36a17a-1f2f-4d26-aecf-bd2e75429b9e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_cf70b0ba-37e3-46bd-9237-3c13f88fcfda" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_de36a17a-1f2f-4d26-aecf-bd2e75429b9e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest_a660890a-bc76-4086-b990-dc6f10f5b8f4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_cf70b0ba-37e3-46bd-9237-3c13f88fcfda" xlink:to="loc_us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest_a660890a-bc76-4086-b990-dc6f10f5b8f4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarningsNetting_41335ae0-0ee0-40c5-b892-4b66490ac877" xlink:href="swx-20250331.xsd#swx_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarningsNetting"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_cf70b0ba-37e3-46bd-9237-3c13f88fcfda" xlink:to="loc_swx_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarningsNetting_41335ae0-0ee0-40c5-b892-4b66490ac877" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStock_d2a03247-6fb9-443f-bfc1-95a0f95064bd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_cf70b0ba-37e3-46bd-9237-3c13f88fcfda" xlink:to="loc_us-gaap_DividendsCommonStock_d2a03247-6fb9-443f-bfc1-95a0f95064bd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTaxOther_05dbe6f1-c038-4097-b942-6da0e8b5ba96" xlink:href="swx-20250331.xsd#swx_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTaxOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_cf70b0ba-37e3-46bd-9237-3c13f88fcfda" xlink:to="loc_swx_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTaxOther_05dbe6f1-c038-4097-b942-6da0e8b5ba96" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_49839ee8-af0a-4142-a1d6-9ed4b79f0dd4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_a7954d65-cdea-4bee-ab7a-98ce2a5d6fdf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#BackgroundOrganizationandSummaryofSignificantAccountingPoliciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_swx_SignificantAccountingPoliciesLineItems_9d5bad94-aafd-4d90-b53a-2997a6747a8a" xlink:href="swx-20250331.xsd#swx_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SignificantAccountingPoliciesTable_021d1c06-250a-4893-acd1-fdda5b9f0a4d" xlink:href="swx-20250331.xsd#swx_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_9d5bad94-aafd-4d90-b53a-2997a6747a8a" xlink:to="loc_swx_SignificantAccountingPoliciesTable_021d1c06-250a-4893-acd1-fdda5b9f0a4d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_a6dcb4ed-f77e-4194-8e92-dcafada862b7" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_swx_SignificantAccountingPoliciesTable_021d1c06-250a-4893-acd1-fdda5b9f0a4d" xlink:to="loc_dei_LegalEntityAxis_a6dcb4ed-f77e-4194-8e92-dcafada862b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a6dcb4ed-f77e-4194-8e92-dcafada862b7_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_a6dcb4ed-f77e-4194-8e92-dcafada862b7" xlink:to="loc_dei_EntityDomain_a6dcb4ed-f77e-4194-8e92-dcafada862b7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_50ffd400-8544-44fc-bbaa-87a393816bd9" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_a6dcb4ed-f77e-4194-8e92-dcafada862b7" xlink:to="loc_dei_EntityDomain_50ffd400-8544-44fc-bbaa-87a393816bd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_6ae773a4-02cb-40ae-8f56-1941eb1dacb7" xlink:href="swx-20250331.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_50ffd400-8544-44fc-bbaa-87a393816bd9" xlink:to="loc_swx_CenturiGroupInc.Member_6ae773a4-02cb-40ae-8f56-1941eb1dacb7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_4acac9ad-450a-41d7-a46e-094e4a46dfa8" xlink:href="swx-20250331.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_50ffd400-8544-44fc-bbaa-87a393816bd9" xlink:to="loc_swx_SouthwestGasCorporationMember_4acac9ad-450a-41d7-a46e-094e4a46dfa8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CertainMembersOfRiggsDistlerManagementMember_b4f46f4f-e7a2-420d-8cbd-f1384b3aeade" xlink:href="swx-20250331.xsd#swx_CertainMembersOfRiggsDistlerManagementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_50ffd400-8544-44fc-bbaa-87a393816bd9" xlink:to="loc_swx_CertainMembersOfRiggsDistlerManagementMember_b4f46f4f-e7a2-420d-8cbd-f1384b3aeade" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_ae2e6bf9-ca56-4b0a-9037-f64e36bcb329" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_swx_SignificantAccountingPoliciesTable_021d1c06-250a-4893-acd1-fdda5b9f0a4d" xlink:to="loc_srt_OwnershipAxis_ae2e6bf9-ca56-4b0a-9037-f64e36bcb329" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_ae2e6bf9-ca56-4b0a-9037-f64e36bcb329_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_ae2e6bf9-ca56-4b0a-9037-f64e36bcb329" xlink:to="loc_srt_OwnershipDomain_ae2e6bf9-ca56-4b0a-9037-f64e36bcb329_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_793fd84f-abda-45af-b5f1-836f315c3b63" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_ae2e6bf9-ca56-4b0a-9037-f64e36bcb329" xlink:to="loc_srt_OwnershipDomain_793fd84f-abda-45af-b5f1-836f315c3b63" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_274e4998-4fd9-4611-af0a-3ff840365ece" xlink:href="swx-20250331.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_793fd84f-abda-45af-b5f1-836f315c3b63" xlink:to="loc_swx_CenturiGroupInc.Member_274e4998-4fd9-4611-af0a-3ff840365ece" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DrumMember_d285f337-5965-44dd-9d41-b5ed6423efed" xlink:href="swx-20250331.xsd#swx_DrumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_793fd84f-abda-45af-b5f1-836f315c3b63" xlink:to="loc_swx_DrumMember_d285f337-5965-44dd-9d41-b5ed6423efed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_0d930688-a6ee-41c3-a717-a452a9e90cdd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_swx_SignificantAccountingPoliciesTable_021d1c06-250a-4893-acd1-fdda5b9f0a4d" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_0d930688-a6ee-41c3-a717-a452a9e90cdd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_0d930688-a6ee-41c3-a717-a452a9e90cdd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_0d930688-a6ee-41c3-a717-a452a9e90cdd" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_0d930688-a6ee-41c3-a717-a452a9e90cdd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_e2d8cd52-1674-4791-ae77-55116935f4d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_0d930688-a6ee-41c3-a717-a452a9e90cdd" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_e2d8cd52-1674-4791-ae77-55116935f4d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_167649bd-cd31-40ef-be60-9904441b8970" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_e2d8cd52-1674-4791-ae77-55116935f4d6" xlink:to="loc_us-gaap_MoneyMarketFundsMember_167649bd-cd31-40ef-be60-9904441b8970" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_28983f18-28d1-4bf2-9267-6397963bd84d" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_swx_SignificantAccountingPoliciesTable_021d1c06-250a-4893-acd1-fdda5b9f0a4d" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_28983f18-28d1-4bf2-9267-6397963bd84d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_28983f18-28d1-4bf2-9267-6397963bd84d_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_28983f18-28d1-4bf2-9267-6397963bd84d" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_28983f18-28d1-4bf2-9267-6397963bd84d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_f6156626-1450-4c81-bb9a-f8ca7b97fbb2" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_28983f18-28d1-4bf2-9267-6397963bd84d" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_f6156626-1450-4c81-bb9a-f8ca7b97fbb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DrumMember_a9998a39-b810-4400-918d-25d43754e2fb" xlink:href="swx-20250331.xsd#swx_DrumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_f6156626-1450-4c81-bb9a-f8ca7b97fbb2" xlink:to="loc_swx_DrumMember_a9998a39-b810-4400-918d-25d43754e2fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_249d8d1f-1046-4cad-8028-65744cf6f4e5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_9d5bad94-aafd-4d90-b53a-2997a6747a8a" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_249d8d1f-1046-4cad-8028-65744cf6f4e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_501ac6df-c97c-4fee-a6fd-881fd81f0e11" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_9d5bad94-aafd-4d90-b53a-2997a6747a8a" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_501ac6df-c97c-4fee-a6fd-881fd81f0e11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CapitalExpendituresIncurredButNotYetPaidIncreaseDecrease_845cc229-7eb5-4dbb-b555-c6465fd7704f" xlink:href="swx-20250331.xsd#swx_CapitalExpendituresIncurredButNotYetPaidIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_9d5bad94-aafd-4d90-b53a-2997a6747a8a" xlink:to="loc_swx_CapitalExpendituresIncurredButNotYetPaidIncreaseDecrease_845cc229-7eb5-4dbb-b555-c6465fd7704f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaterialsSuppliesAndOther_ca094fbf-6e77-4426-9af8-a8d703cc40f2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MaterialsSuppliesAndOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_9d5bad94-aafd-4d90-b53a-2997a6747a8a" xlink:to="loc_us-gaap_MaterialsSuppliesAndOther_ca094fbf-6e77-4426-9af8-a8d703cc40f2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_87778222-f847-43eb-ac53-830097e9226e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_9d5bad94-aafd-4d90-b53a-2997a6747a8a" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_87778222-f847-43eb-ac53-830097e9226e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableCurrent_d9630a86-99e9-4a1f-b373-a699968fca5b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_9d5bad94-aafd-4d90-b53a-2997a6747a8a" xlink:to="loc_us-gaap_DividendsPayableCurrent_d9630a86-99e9-4a1f-b373-a699968fca5b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccruedPurchasedGasCosts_8d7a72ee-3850-4c61-8aac-4fde17b7af14" xlink:href="swx-20250331.xsd#swx_AccruedPurchasedGasCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_9d5bad94-aafd-4d90-b53a-2997a6747a8a" xlink:to="loc_swx_AccruedPurchasedGasCosts_8d7a72ee-3850-4c61-8aac-4fde17b7af14" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DeferredGasCostNet_60ffdfe2-32ea-4795-8d63-efdba5063acb" xlink:href="swx-20250331.xsd#swx_DeferredGasCostNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_9d5bad94-aafd-4d90-b53a-2997a6747a8a" xlink:to="loc_swx_DeferredGasCostNet_60ffdfe2-32ea-4795-8d63-efdba5063acb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTax_ca0d2bb5-f4a9-4867-88d7-6e9fdb1d9182" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherComprehensiveIncomeLossTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_9d5bad94-aafd-4d90-b53a-2997a6747a8a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTax_ca0d2bb5-f4a9-4867-88d7-6e9fdb1d9182" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_3a2a7237-fa76-4653-9e89-d76460e9a77c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_9d5bad94-aafd-4d90-b53a-2997a6747a8a" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_3a2a7237-fa76-4653-9e89-d76460e9a77c" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_1bf03fd0-122d-46e5-bdc7-d70f660821cd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_9d5bad94-aafd-4d90-b53a-2997a6747a8a" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_1bf03fd0-122d-46e5-bdc7-d70f660821cd" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofOtherPropertyandInvestmentsDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofOtherPropertyandInvestmentsDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofOtherPropertyandInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_06fb9e4c-101c-4b58-b964-217eb7e9fa5c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_2419b597-bd72-42a3-a06c-59d34760c6f5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_06fb9e4c-101c-4b58-b964-217eb7e9fa5c" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_2419b597-bd72-42a3-a06c-59d34760c6f5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_f2153f0a-fd01-45a8-8bd1-396e164b67ef" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_2419b597-bd72-42a3-a06c-59d34760c6f5" xlink:to="loc_dei_LegalEntityAxis_f2153f0a-fd01-45a8-8bd1-396e164b67ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_f2153f0a-fd01-45a8-8bd1-396e164b67ef_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_f2153f0a-fd01-45a8-8bd1-396e164b67ef" xlink:to="loc_dei_EntityDomain_f2153f0a-fd01-45a8-8bd1-396e164b67ef_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_9ac30c28-7c71-480a-897a-e2287634bfe6" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_f2153f0a-fd01-45a8-8bd1-396e164b67ef" xlink:to="loc_dei_EntityDomain_9ac30c28-7c71-480a-897a-e2287634bfe6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_22458d79-bc34-40fc-8e2b-272bd6cf9dda" xlink:href="swx-20250331.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_9ac30c28-7c71-480a-897a-e2287634bfe6" xlink:to="loc_swx_SouthwestGasCorporationMember_22458d79-bc34-40fc-8e2b-272bd6cf9dda" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashSurrenderValueOfLifeInsurance_f0d28158-3417-4e30-8aed-cbe788740deb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashSurrenderValueOfLifeInsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_06fb9e4c-101c-4b58-b964-217eb7e9fa5c" xlink:to="loc_us-gaap_CashSurrenderValueOfLifeInsurance_f0d28158-3417-4e30-8aed-cbe788740deb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentOtherNet_677c752a-b89c-4d59-a9bc-bb4cdc71377b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PropertyPlantAndEquipmentOtherNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_06fb9e4c-101c-4b58-b964-217eb7e9fa5c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentOtherNet_677c752a-b89c-4d59-a9bc-bb4cdc71377b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_PropertyPlantEquipmentAndIntangibleAssetsGross_08d5137c-faa6-48ed-89cb-c9ed041b2ca0" xlink:href="swx-20250331.xsd#swx_PropertyPlantEquipmentAndIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_06fb9e4c-101c-4b58-b964-217eb7e9fa5c" xlink:to="loc_swx_PropertyPlantEquipmentAndIntangibleAssetsGross_08d5137c-faa6-48ed-89cb-c9ed041b2ca0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_eff18d48-af84-4ab5-8ae6-44246a49c17d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_06fb9e4c-101c-4b58-b964-217eb7e9fa5c" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_eff18d48-af84-4ab5-8ae6-44246a49c17d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OtherPropertyAndInvestmentsNet_824dd5bd-62d7-45cd-af98-35a89a847b48" xlink:href="swx-20250331.xsd#swx_OtherPropertyAndInvestmentsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_06fb9e4c-101c-4b58-b964-217eb7e9fa5c" xlink:to="loc_swx_OtherPropertyAndInvestmentsNet_824dd5bd-62d7-45cd-af98-35a89a847b48" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofGoodwillDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofGoodwillDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofGoodwillDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_eb68a70d-30ef-4879-9ce6-59612407faff" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_7ab6d98f-19a5-4920-ba41-4445afa202c4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_eb68a70d-30ef-4879-9ce6-59612407faff" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_7ab6d98f-19a5-4920-ba41-4445afa202c4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_b842f00e-aeba-40be-992b-cc1af4e28efa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_7ab6d98f-19a5-4920-ba41-4445afa202c4" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_b842f00e-aeba-40be-992b-cc1af4e28efa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_b842f00e-aeba-40be-992b-cc1af4e28efa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_b842f00e-aeba-40be-992b-cc1af4e28efa" xlink:to="loc_us-gaap_SegmentDomain_b842f00e-aeba-40be-992b-cc1af4e28efa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_c6bb4243-4d0f-40e3-97d1-2386152c5232" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_b842f00e-aeba-40be-992b-cc1af4e28efa" xlink:to="loc_us-gaap_SegmentDomain_c6bb4243-4d0f-40e3-97d1-2386152c5232" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_NaturalGasDistributionSegmentMember_4e13f6da-7bbd-4c4d-9c36-b7eecd444953" xlink:href="swx-20250331.xsd#swx_NaturalGasDistributionSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_c6bb4243-4d0f-40e3-97d1-2386152c5232" xlink:to="loc_swx_NaturalGasDistributionSegmentMember_4e13f6da-7bbd-4c4d-9c36-b7eecd444953" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_UtilityInfrastructureServicesSegmentMember_b3d36154-ddd0-4f1e-90f2-b6ee31df7837" xlink:href="swx-20250331.xsd#swx_UtilityInfrastructureServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_c6bb4243-4d0f-40e3-97d1-2386152c5232" xlink:to="loc_swx_UtilityInfrastructureServicesSegmentMember_b3d36154-ddd0-4f1e-90f2-b6ee31df7837" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillRollForward_da8c9475-416a-41c7-bc4d-668f2674cc4b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_eb68a70d-30ef-4879-9ce6-59612407faff" xlink:to="loc_us-gaap_GoodwillRollForward_da8c9475-416a-41c7-bc4d-668f2674cc4b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_52312ad6-047b-4a02-9bd6-93c7e86160d1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_da8c9475-416a-41c7-bc4d-668f2674cc4b" xlink:to="loc_us-gaap_Goodwill_52312ad6-047b-4a02-9bd6-93c7e86160d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_811bd3f4-3e64-44f5-a7fd-d836b2f24964" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GoodwillForeignCurrencyTranslationGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_da8c9475-416a-41c7-bc4d-668f2674cc4b" xlink:to="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_811bd3f4-3e64-44f5-a7fd-d836b2f24964" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_9e869da6-828c-4d28-bcf1-5f668ff9c2e2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Goodwill"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesOtherIncomeDeductionsDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#BackgroundOrganizationandSummaryofSignificantAccountingPoliciesOtherIncomeDeductionsDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesOtherIncomeDeductionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_srt_CondensedIncomeStatementsCaptionsLineItems_05fe3130-eff9-4ebc-b10c-b6316d25765e" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CondensedIncomeStatementsCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CondensedIncomeStatementTable_1b36649f-7a07-4d55-bb24-34130063971b" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CondensedIncomeStatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_CondensedIncomeStatementsCaptionsLineItems_05fe3130-eff9-4ebc-b10c-b6316d25765e" xlink:to="loc_srt_CondensedIncomeStatementTable_1b36649f-7a07-4d55-bb24-34130063971b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_0027deb2-0ade-4ae4-812b-6ee683087a30" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_CondensedIncomeStatementTable_1b36649f-7a07-4d55-bb24-34130063971b" xlink:to="loc_dei_LegalEntityAxis_0027deb2-0ade-4ae4-812b-6ee683087a30" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_0027deb2-0ade-4ae4-812b-6ee683087a30_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_0027deb2-0ade-4ae4-812b-6ee683087a30" xlink:to="loc_dei_EntityDomain_0027deb2-0ade-4ae4-812b-6ee683087a30_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_bf3fa0d6-34f4-4fc6-b0a7-e9b10be78844" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_0027deb2-0ade-4ae4-812b-6ee683087a30" xlink:to="loc_dei_EntityDomain_bf3fa0d6-34f4-4fc6-b0a7-e9b10be78844" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_94034efe-d1e9-4a13-9c9e-2250ee5404b8" xlink:href="swx-20250331.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_bf3fa0d6-34f4-4fc6-b0a7-e9b10be78844" xlink:to="loc_swx_SouthwestGasCorporationMember_94034efe-d1e9-4a13-9c9e-2250ee5404b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiAndSouthwestGasHoldingsIncMember_eecffdd1-7d6d-41de-97bb-b85b7eee6150" xlink:href="swx-20250331.xsd#swx_CenturiAndSouthwestGasHoldingsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_bf3fa0d6-34f4-4fc6-b0a7-e9b10be78844" xlink:to="loc_swx_CenturiAndSouthwestGasHoldingsIncMember_eecffdd1-7d6d-41de-97bb-b85b7eee6150" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_55028002-5cbc-4e11-8a0f-e8ce4aef4be1" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_CondensedIncomeStatementTable_1b36649f-7a07-4d55-bb24-34130063971b" xlink:to="loc_srt_ConsolidationItemsAxis_55028002-5cbc-4e11-8a0f-e8ce4aef4be1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_55028002-5cbc-4e11-8a0f-e8ce4aef4be1_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_55028002-5cbc-4e11-8a0f-e8ce4aef4be1" xlink:to="loc_srt_ConsolidationItemsDomain_55028002-5cbc-4e11-8a0f-e8ce4aef4be1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_506f842e-ab8e-486f-83bf-5c96863f8cc4" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_55028002-5cbc-4e11-8a0f-e8ce4aef4be1" xlink:to="loc_srt_ConsolidationItemsDomain_506f842e-ab8e-486f-83bf-5c96863f8cc4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_4b17d4e2-9569-4d3b-a40d-2e45fa1ef2b0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_506f842e-ab8e-486f-83bf-5c96863f8cc4" xlink:to="loc_us-gaap_CorporateNonSegmentMember_4b17d4e2-9569-4d3b-a40d-2e45fa1ef2b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_798f2fcc-d566-4325-936a-4aca903c0567" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherNonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedIncomeStatementsCaptionsLineItems_05fe3130-eff9-4ebc-b10c-b6316d25765e" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_798f2fcc-d566-4325-936a-4aca903c0567" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LifeInsuranceCorporateOrBankOwnedChangeInValue_b6a976b4-af84-450a-b53b-884ceec024a5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LifeInsuranceCorporateOrBankOwnedChangeInValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_798f2fcc-d566-4325-936a-4aca903c0567" xlink:to="loc_us-gaap_LifeInsuranceCorporateOrBankOwnedChangeInValue_b6a976b4-af84-450a-b53b-884ceec024a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeOther_5db21d47-42ce-4f25-a10a-84f0569b4586" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestIncomeOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_798f2fcc-d566-4325-936a-4aca903c0567" xlink:to="loc_us-gaap_InterestIncomeOther_5db21d47-42ce-4f25-a10a-84f0569b4586" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity_8d115959-ec39-4244-b75a-29f6855fd28b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_798f2fcc-d566-4325-936a-4aca903c0567" xlink:to="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity_8d115959-ec39-4244-b75a-29f6855fd28b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit_d00f8e08-38fd-4726-82d8-81ba6415bd6c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_798f2fcc-d566-4325-936a-4aca903c0567" xlink:to="loc_us-gaap_DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit_d00f8e08-38fd-4726-82d8-81ba6415bd6c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_MiscellaneousIncomeExpense_6086ced0-ba39-4250-a5b9-e0f32a8952c5" xlink:href="swx-20250331.xsd#swx_MiscellaneousIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_798f2fcc-d566-4325-936a-4aca903c0567" xlink:to="loc_swx_MiscellaneousIncomeExpense_6086ced0-ba39-4250-a5b9-e0f32a8952c5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossRealized_c8c2e0ab-e981-442c-a13b-eca2462e3abf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ForeignCurrencyTransactionGainLossRealized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_798f2fcc-d566-4325-936a-4aca903c0567" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossRealized_c8c2e0ab-e981-442c-a13b-eca2462e3abf" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_68da052e-6177-4e14-b8ea-e9c7ca2136ff" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_798f2fcc-d566-4325-936a-4aca903c0567" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_68da052e-6177-4e14-b8ea-e9c7ca2136ff" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_5d03ecde-f04c-42fb-b51b-069fca8a0c25" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_798f2fcc-d566-4325-936a-4aca903c0567" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_5d03ecde-f04c-42fb-b51b-069fca8a0c25" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofRedeemableNoncontrollingInterestDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofRedeemableNoncontrollingInterestDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofRedeemableNoncontrollingInterestDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_swx_SignificantAccountingPoliciesLineItems_141b8282-c05b-4cc2-92ae-24f0888af73b" xlink:href="swx-20250331.xsd#swx_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SignificantAccountingPoliciesTable_99f0a866-7d96-4342-bf9c-79d6dba6a4ec" xlink:href="swx-20250331.xsd#swx_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_141b8282-c05b-4cc2-92ae-24f0888af73b" xlink:to="loc_swx_SignificantAccountingPoliciesTable_99f0a866-7d96-4342-bf9c-79d6dba6a4ec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_99bcbf72-7d27-4f2f-b2a5-19c6c5087d83" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_swx_SignificantAccountingPoliciesTable_99f0a866-7d96-4342-bf9c-79d6dba6a4ec" xlink:to="loc_srt_OwnershipAxis_99bcbf72-7d27-4f2f-b2a5-19c6c5087d83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_99bcbf72-7d27-4f2f-b2a5-19c6c5087d83_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_99bcbf72-7d27-4f2f-b2a5-19c6c5087d83" xlink:to="loc_srt_OwnershipDomain_99bcbf72-7d27-4f2f-b2a5-19c6c5087d83_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_0816b967-8d61-4bd0-a7f0-7308a96d524f" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_99bcbf72-7d27-4f2f-b2a5-19c6c5087d83" xlink:to="loc_srt_OwnershipDomain_0816b967-8d61-4bd0-a7f0-7308a96d524f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DrumMember_1652ff54-21b8-4d8b-982f-eefb5958e244" xlink:href="swx-20250331.xsd#swx_DrumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_0816b967-8d61-4bd0-a7f0-7308a96d524f" xlink:to="loc_swx_DrumMember_1652ff54-21b8-4d8b-982f-eefb5958e244" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_MovementInRedeemableNoncontrollingInterestRollForward_03b98dae-7e8a-42f0-b5dc-199dfabb4c36" xlink:href="swx-20250331.xsd#swx_MovementInRedeemableNoncontrollingInterestRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_141b8282-c05b-4cc2-92ae-24f0888af73b" xlink:to="loc_swx_MovementInRedeemableNoncontrollingInterestRollForward_03b98dae-7e8a-42f0-b5dc-199dfabb4c36" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_456fedce-442c-49e3-9b68-40ce13e0b8ec" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_MovementInRedeemableNoncontrollingInterestRollForward_03b98dae-7e8a-42f0-b5dc-199dfabb4c36" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_456fedce-442c-49e3-9b68-40ce13e0b8ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_2b284ca0-0bf4-452a-ba16-46a636a48973" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_MovementInRedeemableNoncontrollingInterestRollForward_03b98dae-7e8a-42f0-b5dc-199dfabb4c36" xlink:to="loc_us-gaap_NetIncomeLossAttributableToRedeemableNoncontrollingInterest_2b284ca0-0bf4-452a-ba16-46a636a48973" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_5b892fc5-7521-4f0f-b08e-3ae1beff8c14" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/ComponentsofNetPeriodicBenefitCostDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#ComponentsofNetPeriodicBenefitCostDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/ComponentsofNetPeriodicBenefitCostDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0deafc7b-0ce1-460c-aebc-b74ca21b64d3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_3ab04b0b-a439-48f3-8796-f7a4b5b8209e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0deafc7b-0ce1-460c-aebc-b74ca21b64d3" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_3ab04b0b-a439-48f3-8796-f7a4b5b8209e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_607dc415-3932-4c26-9d29-eabaa1fe805a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_3ab04b0b-a439-48f3-8796-f7a4b5b8209e" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_607dc415-3932-4c26-9d29-eabaa1fe805a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_607dc415-3932-4c26-9d29-eabaa1fe805a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_607dc415-3932-4c26-9d29-eabaa1fe805a" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_607dc415-3932-4c26-9d29-eabaa1fe805a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_f0e1fd97-8542-484b-9676-96842dc70f94" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_607dc415-3932-4c26-9d29-eabaa1fe805a" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_f0e1fd97-8542-484b-9676-96842dc70f94" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPensionPlansDefinedBenefitMember_039b8e20-f4b0-4a0a-a5eb-9ce33d06a46d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherPensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_f0e1fd97-8542-484b-9676-96842dc70f94" xlink:to="loc_us-gaap_OtherPensionPlansDefinedBenefitMember_039b8e20-f4b0-4a0a-a5eb-9ce33d06a46d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember_5571810b-954e-4479-b6af-c6afce7fed89" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_f0e1fd97-8542-484b-9676-96842dc70f94" xlink:to="loc_us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember_5571810b-954e-4479-b6af-c6afce7fed89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_b787be61-e04d-400f-86bb-c2dfc5f6542e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_f0e1fd97-8542-484b-9676-96842dc70f94" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_b787be61-e04d-400f-86bb-c2dfc5f6542e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanServiceCost_cb9679f0-0def-4f74-bcb2-d20fe8716c1e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanServiceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0deafc7b-0ce1-460c-aebc-b74ca21b64d3" xlink:to="loc_us-gaap_DefinedBenefitPlanServiceCost_cb9679f0-0def-4f74-bcb2-d20fe8716c1e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanInterestCost_c7793933-3f24-42a5-ac04-99b4d8db8fe2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanInterestCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0deafc7b-0ce1-460c-aebc-b74ca21b64d3" xlink:to="loc_us-gaap_DefinedBenefitPlanInterestCost_c7793933-3f24-42a5-ac04-99b4d8db8fe2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_957d89b2-dca2-4d39-ba9a-37ebf701adc9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0deafc7b-0ce1-460c-aebc-b74ca21b64d3" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_957d89b2-dca2-4d39-ba9a-37ebf701adc9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_b19dea97-4c90-4ad2-9873-1e21b17d639c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0deafc7b-0ce1-460c-aebc-b74ca21b64d3" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_b19dea97-4c90-4ad2-9873-1e21b17d639c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_d3a0b73f-902a-4266-9924-1e09904598dd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0deafc7b-0ce1-460c-aebc-b74ca21b64d3" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_d3a0b73f-902a-4266-9924-1e09904598dd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_27ea165b-20b5-4062-94ed-0ff982f7e33a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0deafc7b-0ce1-460c-aebc-b74ca21b64d3" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_27ea165b-20b5-4062-94ed-0ff982f7e33a" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/RevenueScheduleofRegulatedOperationsRevenuesNaturalGasDistributionSegmentDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#RevenueScheduleofRegulatedOperationsRevenuesNaturalGasDistributionSegmentDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/RevenueScheduleofRegulatedOperationsRevenuesNaturalGasDistributionSegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_0de5ade8-6f1a-4738-85e8-14c45f4aa331" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_e0610fea-9778-48f6-b3cd-b5bdfc5e0921" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_0de5ade8-6f1a-4738-85e8-14c45f4aa331" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_e0610fea-9778-48f6-b3cd-b5bdfc5e0921" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_b5c9e63a-6309-4a01-97a8-440bf22dbc81" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_e0610fea-9778-48f6-b3cd-b5bdfc5e0921" xlink:to="loc_srt_MajorCustomersAxis_b5c9e63a-6309-4a01-97a8-440bf22dbc81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_b5c9e63a-6309-4a01-97a8-440bf22dbc81_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_b5c9e63a-6309-4a01-97a8-440bf22dbc81" xlink:to="loc_srt_NameOfMajorCustomerDomain_b5c9e63a-6309-4a01-97a8-440bf22dbc81_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_abbb96e4-2ae7-4721-9193-de462419f22b" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_b5c9e63a-6309-4a01-97a8-440bf22dbc81" xlink:to="loc_srt_NameOfMajorCustomerDomain_abbb96e4-2ae7-4721-9193-de462419f22b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_ResidentialMember_fce65fcd-2239-44c4-87cd-b99c8e65c7f7" xlink:href="swx-20250331.xsd#swx_ResidentialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_abbb96e4-2ae7-4721-9193-de462419f22b" xlink:to="loc_swx_ResidentialMember_fce65fcd-2239-44c4-87cd-b99c8e65c7f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SmallCommercialMember_82b5641c-93b4-43cd-b8aa-cb0c948d7a53" xlink:href="swx-20250331.xsd#swx_SmallCommercialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_abbb96e4-2ae7-4721-9193-de462419f22b" xlink:to="loc_swx_SmallCommercialMember_82b5641c-93b4-43cd-b8aa-cb0c948d7a53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_LargeCommercialMember_603d7092-a6fb-4af6-a2c1-12bfc476aad5" xlink:href="swx-20250331.xsd#swx_LargeCommercialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_abbb96e4-2ae7-4721-9193-de462419f22b" xlink:to="loc_swx_LargeCommercialMember_603d7092-a6fb-4af6-a2c1-12bfc476aad5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_IndustrialOrOtherMember_1f25e43d-8702-4339-bf34-0a9c32e91301" xlink:href="swx-20250331.xsd#swx_IndustrialOrOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_abbb96e4-2ae7-4721-9193-de462419f22b" xlink:to="loc_swx_IndustrialOrOtherMember_1f25e43d-8702-4339-bf34-0a9c32e91301" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_TransportationMember_0b1fc714-0bb1-4f3c-88f4-08dd66631ad8" xlink:href="swx-20250331.xsd#swx_TransportationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_abbb96e4-2ae7-4721-9193-de462419f22b" xlink:to="loc_swx_TransportationMember_0b1fc714-0bb1-4f3c-88f4-08dd66631ad8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_11db457e-4faa-4d63-9983-6e917d857451" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_e0610fea-9778-48f6-b3cd-b5bdfc5e0921" xlink:to="loc_dei_LegalEntityAxis_11db457e-4faa-4d63-9983-6e917d857451" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_11db457e-4faa-4d63-9983-6e917d857451_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_11db457e-4faa-4d63-9983-6e917d857451" xlink:to="loc_dei_EntityDomain_11db457e-4faa-4d63-9983-6e917d857451_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_2a56f712-81d4-4451-954a-59e0511aaa4f" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_11db457e-4faa-4d63-9983-6e917d857451" xlink:to="loc_dei_EntityDomain_2a56f712-81d4-4451-954a-59e0511aaa4f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_ccbe5ccb-5309-405d-a7c3-2cf7dc82adb5" xlink:href="swx-20250331.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_2a56f712-81d4-4451-954a-59e0511aaa4f" xlink:to="loc_swx_SouthwestGasCorporationMember_ccbe5ccb-5309-405d-a7c3-2cf7dc82adb5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_978450f4-faa1-4ac5-9118-53ae31c1baf9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_0de5ade8-6f1a-4738-85e8-14c45f4aa331" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_978450f4-faa1-4ac5-9118-53ae31c1baf9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AlternativeRevenueProgramRevenuesDeferrals_4fb597bf-15cd-48ea-9201-786ce40b9892" xlink:href="swx-20250331.xsd#swx_AlternativeRevenueProgramRevenuesDeferrals"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_0de5ade8-6f1a-4738-85e8-14c45f4aa331" xlink:to="loc_swx_AlternativeRevenueProgramRevenuesDeferrals_4fb597bf-15cd-48ea-9201-786ce40b9892" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OtherRevenue_a469a6bd-10fc-49ee-96c6-15fcdf94199c" xlink:href="swx-20250331.xsd#swx_OtherRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_0de5ade8-6f1a-4738-85e8-14c45f4aa331" xlink:to="loc_swx_OtherRevenue_a469a6bd-10fc-49ee-96c6-15fcdf94199c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatedOperatingRevenueGas_0a98b646-5e00-4cb6-9d5c-0da863fc6125" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RegulatedOperatingRevenueGas"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_0de5ade8-6f1a-4738-85e8-14c45f4aa331" xlink:to="loc_us-gaap_RegulatedOperatingRevenueGas_0a98b646-5e00-4cb6-9d5c-0da863fc6125" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/RevenueScheduleofRegulatedOperationsRevenuesUtilityInfrastructureServicesSegmentDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#RevenueScheduleofRegulatedOperationsRevenuesUtilityInfrastructureServicesSegmentDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/RevenueScheduleofRegulatedOperationsRevenuesUtilityInfrastructureServicesSegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_b1b3c2c9-69ac-466d-bbb0-42561406c4f1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_b98ae20e-4171-4902-b57c-82f9fc889e01" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_b1b3c2c9-69ac-466d-bbb0-42561406c4f1" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_b98ae20e-4171-4902-b57c-82f9fc889e01" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_c6360f1f-c457-44dd-8eea-5c18742a536d" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_b98ae20e-4171-4902-b57c-82f9fc889e01" xlink:to="loc_srt_ProductOrServiceAxis_c6360f1f-c457-44dd-8eea-5c18742a536d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_c6360f1f-c457-44dd-8eea-5c18742a536d_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_c6360f1f-c457-44dd-8eea-5c18742a536d" xlink:to="loc_srt_ProductsAndServicesDomain_c6360f1f-c457-44dd-8eea-5c18742a536d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_c5c7daf9-82d4-4128-9908-34613f38c0ff" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_c6360f1f-c457-44dd-8eea-5c18742a536d" xlink:to="loc_srt_ProductsAndServicesDomain_c5c7daf9-82d4-4128-9908-34613f38c0ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_GasInfrastructureServicesMember_8132c791-ad0f-4a04-8171-371b0684bfb5" xlink:href="swx-20250331.xsd#swx_GasInfrastructureServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_c5c7daf9-82d4-4128-9908-34613f38c0ff" xlink:to="loc_swx_GasInfrastructureServicesMember_8132c791-ad0f-4a04-8171-371b0684bfb5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_ElectricPowerInfrastructureServicesMember_e926e5b4-a6bf-4003-9434-75f6a9afbdb4" xlink:href="swx-20250331.xsd#swx_ElectricPowerInfrastructureServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_c5c7daf9-82d4-4128-9908-34613f38c0ff" xlink:to="loc_swx_ElectricPowerInfrastructureServicesMember_e926e5b4-a6bf-4003-9434-75f6a9afbdb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OtherInfrastructureServicesMember_f0eb9257-36b1-418f-9ca7-4084a0901363" xlink:href="swx-20250331.xsd#swx_OtherInfrastructureServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_c5c7daf9-82d4-4128-9908-34613f38c0ff" xlink:to="loc_swx_OtherInfrastructureServicesMember_f0eb9257-36b1-418f-9ca7-4084a0901363" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_d24bb931-7ea6-45d8-9db3-a758d3241d36" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerBasisOfPricingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_b98ae20e-4171-4902-b57c-82f9fc889e01" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_d24bb931-7ea6-45d8-9db3-a758d3241d36" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_d24bb931-7ea6-45d8-9db3-a758d3241d36_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerBasisOfPricingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_d24bb931-7ea6-45d8-9db3-a758d3241d36" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_d24bb931-7ea6-45d8-9db3-a758d3241d36_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_665daa24-4f94-431c-92d9-ab4e9b5a96cb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerBasisOfPricingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_d24bb931-7ea6-45d8-9db3-a758d3241d36" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_665daa24-4f94-431c-92d9-ab4e9b5a96cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_MasterServicesAgreementMember_d6739bd7-bff9-4af5-8816-902a1d3deb24" xlink:href="swx-20250331.xsd#swx_MasterServicesAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_665daa24-4f94-431c-92d9-ab4e9b5a96cb" xlink:to="loc_swx_MasterServicesAgreementMember_d6739bd7-bff9-4af5-8816-902a1d3deb24" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_BidContractMember_76e65259-52d5-4134-baaa-c23388aa3c0b" xlink:href="swx-20250331.xsd#swx_BidContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_665daa24-4f94-431c-92d9-ab4e9b5a96cb" xlink:to="loc_swx_BidContractMember_76e65259-52d5-4134-baaa-c23388aa3c0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_UnitPricedContractsMember_b2f04da6-9a84-4c09-bf6a-2dffb6ba716e" xlink:href="swx-20250331.xsd#swx_UnitPricedContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_665daa24-4f94-431c-92d9-ab4e9b5a96cb" xlink:to="loc_swx_UnitPricedContractsMember_b2f04da6-9a84-4c09-bf6a-2dffb6ba716e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedPriceContractMember_ae764316-9d9f-4396-9b47-b969559d8e04" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FixedPriceContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_665daa24-4f94-431c-92d9-ab4e9b5a96cb" xlink:to="loc_us-gaap_FixedPriceContractMember_ae764316-9d9f-4396-9b47-b969559d8e04" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimeAndMaterialsContractMember_3de09321-5531-462c-9518-6e60e7447e95" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TimeAndMaterialsContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_665daa24-4f94-431c-92d9-ab4e9b5a96cb" xlink:to="loc_us-gaap_TimeAndMaterialsContractMember_3de09321-5531-462c-9518-6e60e7447e95" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_4071ed63-7bf5-41a6-a60e-810b091b6e8c" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_b98ae20e-4171-4902-b57c-82f9fc889e01" xlink:to="loc_dei_LegalEntityAxis_4071ed63-7bf5-41a6-a60e-810b091b6e8c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_4071ed63-7bf5-41a6-a60e-810b091b6e8c_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_4071ed63-7bf5-41a6-a60e-810b091b6e8c" xlink:to="loc_dei_EntityDomain_4071ed63-7bf5-41a6-a60e-810b091b6e8c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_98d5f8d8-e55f-40db-a38d-be87a0e4fcc3" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_4071ed63-7bf5-41a6-a60e-810b091b6e8c" xlink:to="loc_dei_EntityDomain_98d5f8d8-e55f-40db-a38d-be87a0e4fcc3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_d1cce699-a482-4030-8b62-b43eb42d9f67" xlink:href="swx-20250331.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_98d5f8d8-e55f-40db-a38d-be87a0e4fcc3" xlink:to="loc_swx_CenturiGroupInc.Member_d1cce699-a482-4030-8b62-b43eb42d9f67" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_16128e4b-046e-41e4-8c18-b28bd9b0c2d3" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_b98ae20e-4171-4902-b57c-82f9fc889e01" xlink:to="loc_srt_RestatementAxis_16128e4b-046e-41e4-8c18-b28bd9b0c2d3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_16128e4b-046e-41e4-8c18-b28bd9b0c2d3_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_16128e4b-046e-41e4-8c18-b28bd9b0c2d3" xlink:to="loc_srt_RestatementDomain_16128e4b-046e-41e4-8c18-b28bd9b0c2d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_9224aa3f-e70f-4dcc-bcbd-c706aef043e7" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_16128e4b-046e-41e4-8c18-b28bd9b0c2d3" xlink:to="loc_srt_RestatementDomain_9224aa3f-e70f-4dcc-bcbd-c706aef043e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioPreviouslyReportedMember_03a55144-518e-4eb4-836b-5e7fe24fe58e" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ScenarioPreviouslyReportedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_9224aa3f-e70f-4dcc-bcbd-c706aef043e7" xlink:to="loc_srt_ScenarioPreviouslyReportedMember_03a55144-518e-4eb4-836b-5e7fe24fe58e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_e4c7726c-b0fe-429e-99ec-da6d253cf600" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_b1b3c2c9-69ac-466d-bbb0-42561406c4f1" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_e4c7726c-b0fe-429e-99ec-da6d253cf600" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/RevenueNarrativeDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#RevenueNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/RevenueNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_33648174-78be-4adb-8d51-4205a80be4f7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_33648174-78be-4adb-8d51-4205a80be4f7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_d7f444d8-c9dc-440c-af2d-9d3b323701d7" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_33648174-78be-4adb-8d51-4205a80be4f7" xlink:to="loc_dei_LegalEntityAxis_d7f444d8-c9dc-440c-af2d-9d3b323701d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_d7f444d8-c9dc-440c-af2d-9d3b323701d7_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_d7f444d8-c9dc-440c-af2d-9d3b323701d7" xlink:to="loc_dei_EntityDomain_d7f444d8-c9dc-440c-af2d-9d3b323701d7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_e80e4901-0934-4de1-aeab-aa4784b27175" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_d7f444d8-c9dc-440c-af2d-9d3b323701d7" xlink:to="loc_dei_EntityDomain_e80e4901-0934-4de1-aeab-aa4784b27175" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_4e5515e6-3b2e-485c-8ef5-75722f678376" xlink:href="swx-20250331.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_e80e4901-0934-4de1-aeab-aa4784b27175" xlink:to="loc_swx_CenturiGroupInc.Member_4e5515e6-3b2e-485c-8ef5-75722f678376" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_3840725f-a2e9-445f-ac7b-856d9ebc7f26" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_33648174-78be-4adb-8d51-4205a80be4f7" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_3840725f-a2e9-445f-ac7b-856d9ebc7f26" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerReceivableAllowanceForCreditLossNoncurrent_5e3934ac-549c-47db-9957-25cdf6058f00" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerReceivableAllowanceForCreditLossNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_ContractWithCustomerReceivableAllowanceForCreditLossNoncurrent_5e3934ac-549c-47db-9957-25cdf6058f00" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerAsset_9aacd352-2d94-44a7-8001-9ee77ff071fc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerAsset_9aacd352-2d94-44a7-8001-9ee77ff071fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetAllowanceForCreditLossRecovery_5f58f778-5d1c-4b2c-814a-ea1ef8c445fe" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerAssetAllowanceForCreditLossRecovery"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_ContractWithCustomerAssetAllowanceForCreditLossRecovery_5f58f778-5d1c-4b2c-814a-ea1ef8c445fe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_c4f19872-b197-4e88-852c-4d8e457ede34" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_c4f19872-b197-4e88-852c-4d8e457ede34" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_b551db67-47cc-441e-9b7e-003feb9eba89" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_b551db67-47cc-441e-9b7e-003feb9eba89" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_RevenueRecognitionNumberOfContractsWithOriginalDurationMoreThanOneYear_f3c2734c-fd5b-4cf9-a121-a4ccc27b6596" xlink:href="swx-20250331.xsd#swx_RevenueRecognitionNumberOfContractsWithOriginalDurationMoreThanOneYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_swx_RevenueRecognitionNumberOfContractsWithOriginalDurationMoreThanOneYear_f3c2734c-fd5b-4cf9-a121-a4ccc27b6596" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_0e643d34-7c3a-4ff6-ab9c-f00e42aab367" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_0e643d34-7c3a-4ff6-ab9c-f00e42aab367" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_c53bd557-dcb1-49f4-a616-161d1ac2aa87" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_c53bd557-dcb1-49f4-a616-161d1ac2aa87" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccountsReceivableSecuritizationTerm_042369c9-efc1-43fb-a143-c35bb2a45bf9" xlink:href="swx-20250331.xsd#swx_AccountsReceivableSecuritizationTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_swx_AccountsReceivableSecuritizationTerm_042369c9-efc1-43fb-a143-c35bb2a45bf9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccountsReceivableSecuritizationMaximumAmountAuthorized_a25c3684-c289-4dae-8767-6209baca150f" xlink:href="swx-20250331.xsd#swx_AccountsReceivableSecuritizationMaximumAmountAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_swx_AccountsReceivableSecuritizationMaximumAmountAuthorized_a25c3684-c289-4dae-8767-6209baca150f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableFromSecuritization_a9bf7607-d834-4880-91a0-c915b4dfba38" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsReceivableFromSecuritization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_AccountsReceivableFromSecuritization_a9bf7607-d834-4880-91a0-c915b4dfba38" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccountsReceivableSecuritizationUnsoldReceivables_1598d413-6a1a-47e7-b5f2-717e276ec1c3" xlink:href="swx-20250331.xsd#swx_AccountsReceivableSecuritizationUnsoldReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_swx_AccountsReceivableSecuritizationUnsoldReceivables_1598d413-6a1a-47e7-b5f2-717e276ec1c3" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccountsReceivableSecuritizationContractAssets_a403d10a-3421-4a8c-ac85-7115847da0bd" xlink:href="swx-20250331.xsd#swx_AccountsReceivableSecuritizationContractAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_swx_AccountsReceivableSecuritizationContractAssets_a403d10a-3421-4a8c-ac85-7115847da0bd" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromAccountsReceivableSecuritization_e96aa631-ac12-4042-a464-437fd09c077d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromAccountsReceivableSecuritization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_ProceedsFromAccountsReceivableSecuritization_e96aa631-ac12-4042-a464-437fd09c077d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfAccountsReceivableSecuritization_1c628b8d-d98e-4c51-b1cf-0eb2356664f7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RepaymentsOfAccountsReceivableSecuritization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_RepaymentsOfAccountsReceivableSecuritization_1c628b8d-d98e-4c51-b1cf-0eb2356664f7" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccountsReceivableSecuritizationRemainingAmountAuthorized_3043a66c-9e83-4925-a4dc-89a9e1b18e71" xlink:href="swx-20250331.xsd#swx_AccountsReceivableSecuritizationRemainingAmountAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_swx_AccountsReceivableSecuritizationRemainingAmountAuthorized_3043a66c-9e83-4925-a4dc-89a9e1b18e71" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/RevenueNarrativeDetails_1" xlink:type="simple" xlink:href="swx-20250331.xsd#RevenueNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/RevenueNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_33648174-78be-4adb-8d51-4205a80be4f7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_33648174-78be-4adb-8d51-4205a80be4f7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_d7f444d8-c9dc-440c-af2d-9d3b323701d7" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_33648174-78be-4adb-8d51-4205a80be4f7" xlink:to="loc_dei_LegalEntityAxis_d7f444d8-c9dc-440c-af2d-9d3b323701d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_d7f444d8-c9dc-440c-af2d-9d3b323701d7_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_d7f444d8-c9dc-440c-af2d-9d3b323701d7" xlink:to="loc_dei_EntityDomain_d7f444d8-c9dc-440c-af2d-9d3b323701d7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_e80e4901-0934-4de1-aeab-aa4784b27175" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_d7f444d8-c9dc-440c-af2d-9d3b323701d7" xlink:to="loc_dei_EntityDomain_e80e4901-0934-4de1-aeab-aa4784b27175" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_4e5515e6-3b2e-485c-8ef5-75722f678376" xlink:href="swx-20250331.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_e80e4901-0934-4de1-aeab-aa4784b27175" xlink:to="loc_swx_CenturiGroupInc.Member_4e5515e6-3b2e-485c-8ef5-75722f678376" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerReceivableAllowanceForCreditLossNoncurrent_5e3934ac-549c-47db-9957-25cdf6058f00" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerReceivableAllowanceForCreditLossNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_ContractWithCustomerReceivableAllowanceForCreditLossNoncurrent_5e3934ac-549c-47db-9957-25cdf6058f00" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerAsset_9aacd352-2d94-44a7-8001-9ee77ff071fc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerAsset_9aacd352-2d94-44a7-8001-9ee77ff071fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetAllowanceForCreditLossRecovery_5f58f778-5d1c-4b2c-814a-ea1ef8c445fe" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerAssetAllowanceForCreditLossRecovery"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_ContractWithCustomerAssetAllowanceForCreditLossRecovery_5f58f778-5d1c-4b2c-814a-ea1ef8c445fe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_c4f19872-b197-4e88-852c-4d8e457ede34" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_c4f19872-b197-4e88-852c-4d8e457ede34" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_b551db67-47cc-441e-9b7e-003feb9eba89" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_b551db67-47cc-441e-9b7e-003feb9eba89" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_RevenueRecognitionNumberOfContractsWithOriginalDurationMoreThanOneYear_f3c2734c-fd5b-4cf9-a121-a4ccc27b6596" xlink:href="swx-20250331.xsd#swx_RevenueRecognitionNumberOfContractsWithOriginalDurationMoreThanOneYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_swx_RevenueRecognitionNumberOfContractsWithOriginalDurationMoreThanOneYear_f3c2734c-fd5b-4cf9-a121-a4ccc27b6596" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_0e643d34-7c3a-4ff6-ab9c-f00e42aab367" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_0e643d34-7c3a-4ff6-ab9c-f00e42aab367" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_c53bd557-dcb1-49f4-a616-161d1ac2aa87" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_c53bd557-dcb1-49f4-a616-161d1ac2aa87" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccountsReceivableSecuritizationTerm_042369c9-efc1-43fb-a143-c35bb2a45bf9" xlink:href="swx-20250331.xsd#swx_AccountsReceivableSecuritizationTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_swx_AccountsReceivableSecuritizationTerm_042369c9-efc1-43fb-a143-c35bb2a45bf9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccountsReceivableSecuritizationMaximumAmountAuthorized_a25c3684-c289-4dae-8767-6209baca150f" xlink:href="swx-20250331.xsd#swx_AccountsReceivableSecuritizationMaximumAmountAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_swx_AccountsReceivableSecuritizationMaximumAmountAuthorized_a25c3684-c289-4dae-8767-6209baca150f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableFromSecuritization_a9bf7607-d834-4880-91a0-c915b4dfba38" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsReceivableFromSecuritization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_AccountsReceivableFromSecuritization_a9bf7607-d834-4880-91a0-c915b4dfba38" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccountsReceivableSecuritizationUnsoldReceivables_1598d413-6a1a-47e7-b5f2-717e276ec1c3" xlink:href="swx-20250331.xsd#swx_AccountsReceivableSecuritizationUnsoldReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_swx_AccountsReceivableSecuritizationUnsoldReceivables_1598d413-6a1a-47e7-b5f2-717e276ec1c3" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccountsReceivableSecuritizationContractAssets_a403d10a-3421-4a8c-ac85-7115847da0bd" xlink:href="swx-20250331.xsd#swx_AccountsReceivableSecuritizationContractAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_swx_AccountsReceivableSecuritizationContractAssets_a403d10a-3421-4a8c-ac85-7115847da0bd" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromAccountsReceivableSecuritization_e96aa631-ac12-4042-a464-437fd09c077d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromAccountsReceivableSecuritization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_ProceedsFromAccountsReceivableSecuritization_e96aa631-ac12-4042-a464-437fd09c077d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfAccountsReceivableSecuritization_1c628b8d-d98e-4c51-b1cf-0eb2356664f7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RepaymentsOfAccountsReceivableSecuritization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_us-gaap_RepaymentsOfAccountsReceivableSecuritization_1c628b8d-d98e-4c51-b1cf-0eb2356664f7" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccountsReceivableSecuritizationRemainingAmountAuthorized_3043a66c-9e83-4925-a4dc-89a9e1b18e71" xlink:href="swx-20250331.xsd#swx_AccountsReceivableSecuritizationRemainingAmountAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_ae702380-8bcf-4b92-b666-bb02bb5f56c1" xlink:to="loc_swx_AccountsReceivableSecuritizationRemainingAmountAuthorized_3043a66c-9e83-4925-a4dc-89a9e1b18e71" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/RevenueScheduleofUtilityInfrastructureServicesContractsReceivableDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#RevenueScheduleofUtilityInfrastructureServicesContractsReceivableDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/RevenueScheduleofUtilityInfrastructureServicesContractsReceivableDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_01e6e272-cc44-4840-9745-ca95a056ed86" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_0ba10204-f4c5-49da-b3c6-49fadc4d4771" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01e6e272-cc44-4840-9745-ca95a056ed86" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_0ba10204-f4c5-49da-b3c6-49fadc4d4771" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_bac941fb-66d0-4ac3-9ed4-4efae2aeb4bf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_0ba10204-f4c5-49da-b3c6-49fadc4d4771" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_bac941fb-66d0-4ac3-9ed4-4efae2aeb4bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_bac941fb-66d0-4ac3-9ed4-4efae2aeb4bf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_bac941fb-66d0-4ac3-9ed4-4efae2aeb4bf" xlink:to="loc_us-gaap_SegmentDomain_bac941fb-66d0-4ac3-9ed4-4efae2aeb4bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_14eebaca-7c15-4ce3-85da-3e893efc1fac" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_bac941fb-66d0-4ac3-9ed4-4efae2aeb4bf" xlink:to="loc_us-gaap_SegmentDomain_14eebaca-7c15-4ce3-85da-3e893efc1fac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_UtilityInfrastructureServicesSegmentMember_23c0fdd8-4f2a-4625-a85c-3fec5472ec37" xlink:href="swx-20250331.xsd#swx_UtilityInfrastructureServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_14eebaca-7c15-4ce3-85da-3e893efc1fac" xlink:to="loc_swx_UtilityInfrastructureServicesSegmentMember_23c0fdd8-4f2a-4625-a85c-3fec5472ec37" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_8e3c787d-ed02-4f0c-868a-20ca9deeb735" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_0ba10204-f4c5-49da-b3c6-49fadc4d4771" xlink:to="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_8e3c787d-ed02-4f0c-868a-20ca9deeb735" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_8e3c787d-ed02-4f0c-868a-20ca9deeb735_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_8e3c787d-ed02-4f0c-868a-20ca9deeb735" xlink:to="loc_us-gaap_ReceivableTypeDomain_8e3c787d-ed02-4f0c-868a-20ca9deeb735_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_9c676d07-925b-401a-89ee-3400f247b994" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_8e3c787d-ed02-4f0c-868a-20ca9deeb735" xlink:to="loc_us-gaap_ReceivableTypeDomain_9c676d07-925b-401a-89ee-3400f247b994" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_BilledOnCompletedContractsAndContractsInProgressMember_d9ad10d5-c902-4041-a0f0-9e018d3bc8f3" xlink:href="swx-20250331.xsd#swx_BilledOnCompletedContractsAndContractsInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivableTypeDomain_9c676d07-925b-401a-89ee-3400f247b994" xlink:to="loc_swx_BilledOnCompletedContractsAndContractsInProgressMember_d9ad10d5-c902-4041-a0f0-9e018d3bc8f3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OtherReceivablesMember_f8d76fa3-5652-4a6e-8b63-04a89e7b46b2" xlink:href="swx-20250331.xsd#swx_OtherReceivablesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivableTypeDomain_9c676d07-925b-401a-89ee-3400f247b994" xlink:to="loc_swx_OtherReceivablesMember_f8d76fa3-5652-4a6e-8b63-04a89e7b46b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetGross_3bc20c8c-f188-4764-b58c-828272257984" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerAssetGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01e6e272-cc44-4840-9745-ca95a056ed86" xlink:to="loc_us-gaap_ContractWithCustomerAssetGross_3bc20c8c-f188-4764-b58c-828272257984" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss_f440fb3d-877d-4d60-81c6-30ae7630ca82" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01e6e272-cc44-4840-9745-ca95a056ed86" xlink:to="loc_us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss_f440fb3d-877d-4d60-81c6-30ae7630ca82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNet_30355eb0-6e8a-4cd0-b4fc-e9bc915dc3a9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ContractWithCustomerAssetNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_01e6e272-cc44-4840-9745-ca95a056ed86" xlink:to="loc_us-gaap_ContractWithCustomerAssetNet_30355eb0-6e8a-4cd0-b4fc-e9bc915dc3a9" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/CommonStockDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#CommonStockDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CommonStockDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_4e91366f-1ec2-49ae-825d-00f1b7532adf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_00dcf2db-4793-4a97-a674-216e3a81716e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_4e91366f-1ec2-49ae-825d-00f1b7532adf" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_00dcf2db-4793-4a97-a674-216e3a81716e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_d485715a-c565-41e3-994a-00f753535b9e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_00dcf2db-4793-4a97-a674-216e3a81716e" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_d485715a-c565-41e3-994a-00f753535b9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_d485715a-c565-41e3-994a-00f753535b9e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_d485715a-c565-41e3-994a-00f753535b9e" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_d485715a-c565-41e3-994a-00f753535b9e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_cda6fbd6-f90f-4212-9445-f75bfb4c5bca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_d485715a-c565-41e3-994a-00f753535b9e" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_cda6fbd6-f90f-4212-9445-f75bfb4c5bca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_ATMProgramMember_fcbf522a-eae9-4267-aebf-ce17542e94f4" xlink:href="swx-20250331.xsd#swx_ATMProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_cda6fbd6-f90f-4212-9445-f75bfb4c5bca" xlink:to="loc_swx_ATMProgramMember_fcbf522a-eae9-4267-aebf-ce17542e94f4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SaleOfStockMaximumConsiderationToBeReceivedOnTransaction_4acfabb9-ba61-4888-8446-13b70066eb99" xlink:href="swx-20250331.xsd#swx_SaleOfStockMaximumConsiderationToBeReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_4e91366f-1ec2-49ae-825d-00f1b7532adf" xlink:to="loc_swx_SaleOfStockMaximumConsiderationToBeReceivedOnTransaction_4acfabb9-ba61-4888-8446-13b70066eb99" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/DebtScheduleofCarryingAmountsandEstimatedFairValuesofLongTermDebtDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#DebtScheduleofCarryingAmountsandEstimatedFairValuesofLongTermDebtDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/DebtScheduleofCarryingAmountsandEstimatedFairValuesofLongTermDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_d2d1dd64-0850-4db4-aa50-97517000a4ce" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_a051226d-8106-45a7-843f-73ff04d80017" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d2d1dd64-0850-4db4-aa50-97517000a4ce" xlink:to="loc_us-gaap_DebtInstrumentTable_a051226d-8106-45a7-843f-73ff04d80017" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_04fc1614-5799-4b5f-a633-f059fbb5d307" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a051226d-8106-45a7-843f-73ff04d80017" xlink:to="loc_us-gaap_DebtInstrumentAxis_04fc1614-5799-4b5f-a633-f059fbb5d307" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_04fc1614-5799-4b5f-a633-f059fbb5d307_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_04fc1614-5799-4b5f-a633-f059fbb5d307" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_04fc1614-5799-4b5f-a633-f059fbb5d307_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_04fc1614-5799-4b5f-a633-f059fbb5d307" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_Debentures8SeriesDue2026Member_7a2d6513-9c91-48e1-b738-2fab8cf02986" xlink:href="swx-20250331.xsd#swx_Debentures8SeriesDue2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_Debentures8SeriesDue2026Member_7a2d6513-9c91-48e1-b738-2fab8cf02986" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesMediumTermNotes7.92SeriesDue2027Member_74cea5bb-2717-4c53-bcc1-cc128e62141d" xlink:href="swx-20250331.xsd#swx_DebenturesMediumTermNotes7.92SeriesDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_DebenturesMediumTermNotes7.92SeriesDue2027Member_74cea5bb-2717-4c53-bcc1-cc128e62141d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesMediumTermNotes6.76SeriesDue2027Member_9dd19743-b58e-4bcc-bcf8-2c5b44ff8237" xlink:href="swx-20250331.xsd#swx_DebenturesMediumTermNotes6.76SeriesDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_DebenturesMediumTermNotes6.76SeriesDue2027Member_9dd19743-b58e-4bcc-bcf8-2c5b44ff8237" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotes5.8Due2027Member_36289b1a-889a-4e97-820f-c6a8fc0cce08" xlink:href="swx-20250331.xsd#swx_DebenturesNotes5.8Due2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_DebenturesNotes5.8Due2027Member_36289b1a-889a-4e97-820f-c6a8fc0cce08" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotes3.7Due2028Member_03ee2fb2-1805-4ab4-bc2d-a3c0e9c7fdab" xlink:href="swx-20250331.xsd#swx_DebenturesNotes3.7Due2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_DebenturesNotes3.7Due2028Member_03ee2fb2-1805-4ab4-bc2d-a3c0e9c7fdab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotes5.45Due2028Member_b4bf063d-2295-4393-bd00-8d0432cc47f1" xlink:href="swx-20250331.xsd#swx_DebenturesNotes5.45Due2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_DebenturesNotes5.45Due2028Member_b4bf063d-2295-4393-bd00-8d0432cc47f1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotes2.2Due2030Member_798813cb-ddbf-4604-986f-bd7a6a526610" xlink:href="swx-20250331.xsd#swx_DebenturesNotes2.2Due2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_DebenturesNotes2.2Due2030Member_798813cb-ddbf-4604-986f-bd7a6a526610" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotes4.05Due2032Member_c4ddd17b-e55a-4eec-b306-167ff87a4f4c" xlink:href="swx-20250331.xsd#swx_DebenturesNotes4.05Due2032Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_DebenturesNotes4.05Due2032Member_c4ddd17b-e55a-4eec-b306-167ff87a4f4c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotes6.1Due2041Member_f0ad82ad-882a-4a2c-ae44-b6a75b2c1139" xlink:href="swx-20250331.xsd#swx_DebenturesNotes6.1Due2041Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_DebenturesNotes6.1Due2041Member_f0ad82ad-882a-4a2c-ae44-b6a75b2c1139" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotes4.875Due2043Member_25b02930-97ee-435d-a731-cf28e8080fba" xlink:href="swx-20250331.xsd#swx_DebenturesNotes4.875Due2043Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_DebenturesNotes4.875Due2043Member_25b02930-97ee-435d-a731-cf28e8080fba" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotes3.8Due2046Member_1ec74186-107c-45d2-8e52-e32b45353016" xlink:href="swx-20250331.xsd#swx_DebenturesNotes3.8Due2046Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_DebenturesNotes3.8Due2046Member_1ec74186-107c-45d2-8e52-e32b45353016" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotes4.15Due2049Member_8ce69311-febc-49e1-89ae-98f16b66dfd4" xlink:href="swx-20250331.xsd#swx_DebenturesNotes4.15Due2049Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_DebenturesNotes4.15Due2049Member_8ce69311-febc-49e1-89ae-98f16b66dfd4" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotes3.18Due2051Member_53bed558-9921-42d6-a92f-fa46f27f3fdb" xlink:href="swx-20250331.xsd#swx_DebenturesNotes3.18Due2051Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_DebenturesNotes3.18Due2051Member_53bed558-9921-42d6-a92f-fa46f27f3fdb" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_VariableRateBondsTaxExemptSeriesADue2028Member_2e28390a-e28e-4221-aca5-6ee812ed6933" xlink:href="swx-20250331.xsd#swx_VariableRateBondsTaxExemptSeriesADue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_VariableRateBondsTaxExemptSeriesADue2028Member_2e28390a-e28e-4221-aca5-6ee812ed6933" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_VariableRateBonds2003SeriesADue2038Member_f8d7f519-b638-4979-b94f-63b379c9d242" xlink:href="swx-20250331.xsd#swx_VariableRateBonds2003SeriesADue2038Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_VariableRateBonds2003SeriesADue2038Member_f8d7f519-b638-4979-b94f-63b379c9d242" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_VariableRateBonds2008SeriesADue2038Member_3b19f3fa-1c3e-4e34-8514-5210dcfab71f" xlink:href="swx-20250331.xsd#swx_VariableRateBonds2008SeriesADue2038Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_VariableRateBonds2008SeriesADue2038Member_3b19f3fa-1c3e-4e34-8514-5210dcfab71f" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_VariableRateBonds2009SeriesADue2039Member_b6ede5b7-a8fa-4ba7-b445-a3c33f6e8b98" xlink:href="swx-20250331.xsd#swx_VariableRateBonds2009SeriesADue2039Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_VariableRateBonds2009SeriesADue2039Member_b6ede5b7-a8fa-4ba7-b445-a3c33f6e8b98" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiSecuredTermLoanFacilityMember_7eb268e4-b6e8-4efa-849e-b8f8b400a873" xlink:href="swx-20250331.xsd#swx_CenturiSecuredTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c2efc671-a104-4153-beeb-45d73d9e2451" xlink:to="loc_swx_CenturiSecuredTermLoanFacilityMember_7eb268e4-b6e8-4efa-849e-b8f8b400a873" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_17186240-e218-41e0-b216-1f5f893892e5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a051226d-8106-45a7-843f-73ff04d80017" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_17186240-e218-41e0-b216-1f5f893892e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_17186240-e218-41e0-b216-1f5f893892e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_17186240-e218-41e0-b216-1f5f893892e5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_17186240-e218-41e0-b216-1f5f893892e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_90c6d392-197c-4dff-9ecf-76e0dfadbf99" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_17186240-e218-41e0-b216-1f5f893892e5" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_90c6d392-197c-4dff-9ecf-76e0dfadbf99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesMember_8dbcf697-d4be-4e62-8697-1bb2b58f56f7" xlink:href="swx-20250331.xsd#swx_DebenturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_90c6d392-197c-4dff-9ecf-76e0dfadbf99" xlink:to="loc_swx_DebenturesMember_8dbcf697-d4be-4e62-8697-1bb2b58f56f7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_RevolvingCreditFacilityAndCommercialPaperMember_40b65d60-5541-4549-a49c-8ad88ec7b901" xlink:href="swx-20250331.xsd#swx_RevolvingCreditFacilityAndCommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_90c6d392-197c-4dff-9ecf-76e0dfadbf99" xlink:to="loc_swx_RevolvingCreditFacilityAndCommercialPaperMember_40b65d60-5541-4549-a49c-8ad88ec7b901" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_IndustrialDevelopmentRevenueBondsMember_bb50c342-c3b7-4edb-8ce7-c670c91c8a85" xlink:href="swx-20250331.xsd#swx_IndustrialDevelopmentRevenueBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_90c6d392-197c-4dff-9ecf-76e0dfadbf99" xlink:to="loc_swx_IndustrialDevelopmentRevenueBondsMember_bb50c342-c3b7-4edb-8ce7-c670c91c8a85" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_8e8eb5b0-bf82-4ff8-aef8-83aca4a0eb78" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_90c6d392-197c-4dff-9ecf-76e0dfadbf99" xlink:to="loc_us-gaap_SecuredDebtMember_8e8eb5b0-bf82-4ff8-aef8-83aca4a0eb78" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherDebtSecuritiesMember_570b04e8-0abf-4684-9a90-54f5217aa670" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_90c6d392-197c-4dff-9ecf-76e0dfadbf99" xlink:to="loc_us-gaap_OtherDebtSecuritiesMember_570b04e8-0abf-4684-9a90-54f5217aa670" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_c0b81efd-0e94-46b8-9508-66d484cdf4f6" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a051226d-8106-45a7-843f-73ff04d80017" xlink:to="loc_dei_LegalEntityAxis_c0b81efd-0e94-46b8-9508-66d484cdf4f6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_c0b81efd-0e94-46b8-9508-66d484cdf4f6_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_c0b81efd-0e94-46b8-9508-66d484cdf4f6" xlink:to="loc_dei_EntityDomain_c0b81efd-0e94-46b8-9508-66d484cdf4f6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_216a8aea-f722-4218-ac03-4000fc08c962" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_c0b81efd-0e94-46b8-9508-66d484cdf4f6" xlink:to="loc_dei_EntityDomain_216a8aea-f722-4218-ac03-4000fc08c962" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_0b49878c-599e-469f-8466-293f08642203" xlink:href="swx-20250331.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_216a8aea-f722-4218-ac03-4000fc08c962" xlink:to="loc_swx_SouthwestGasCorporationMember_0b49878c-599e-469f-8466-293f08642203" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_12edaea8-0eb6-4214-a7b5-376489de4125" xlink:href="swx-20250331.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_216a8aea-f722-4218-ac03-4000fc08c962" xlink:to="loc_swx_CenturiGroupInc.Member_12edaea8-0eb6-4214-a7b5-376489de4125" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_b7a7a405-58e5-46a9-9de8-4c031a35df6d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a051226d-8106-45a7-843f-73ff04d80017" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_b7a7a405-58e5-46a9-9de8-4c031a35df6d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_b7a7a405-58e5-46a9-9de8-4c031a35df6d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_b7a7a405-58e5-46a9-9de8-4c031a35df6d" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_b7a7a405-58e5-46a9-9de8-4c031a35df6d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_1d68aeff-c9c9-4259-b8f6-c1c3bfe58dde" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_b7a7a405-58e5-46a9-9de8-4c031a35df6d" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_1d68aeff-c9c9-4259-b8f6-c1c3bfe58dde" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_46ed9227-9d80-41ec-874e-e00550a6856b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_1d68aeff-c9c9-4259-b8f6-c1c3bfe58dde" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_46ed9227-9d80-41ec-874e-e00550a6856b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_b26ba2df-05d6-48ed-8377-35bebf4c71d1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_46ed9227-9d80-41ec-874e-e00550a6856b" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_b26ba2df-05d6-48ed-8377-35bebf4c71d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_6acf088f-98be-4073-b75b-73a4a28f335c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_46ed9227-9d80-41ec-874e-e00550a6856b" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_6acf088f-98be-4073-b75b-73a4a28f335c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_ecf5dcad-e9b7-49a3-89c3-c1cdf4cd64b2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_a051226d-8106-45a7-843f-73ff04d80017" xlink:to="loc_us-gaap_CreditFacilityAxis_ecf5dcad-e9b7-49a3-89c3-c1cdf4cd64b2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_ecf5dcad-e9b7-49a3-89c3-c1cdf4cd64b2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_ecf5dcad-e9b7-49a3-89c3-c1cdf4cd64b2" xlink:to="loc_us-gaap_CreditFacilityDomain_ecf5dcad-e9b7-49a3-89c3-c1cdf4cd64b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_300764bc-1252-4d83-b9d0-f30508c11667" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_ecf5dcad-e9b7-49a3-89c3-c1cdf4cd64b2" xlink:to="loc_us-gaap_CreditFacilityDomain_300764bc-1252-4d83-b9d0-f30508c11667" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiSecuredRevolvingCreditFacilityMember_a145a6ee-755c-434b-916e-f04530412b84" xlink:href="swx-20250331.xsd#swx_CenturiSecuredRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_300764bc-1252-4d83-b9d0-f30508c11667" xlink:to="loc_swx_CenturiSecuredRevolvingCreditFacilityMember_a145a6ee-755c-434b-916e-f04530412b84" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_4e5bb5ad-c936-4138-a71e-cf352774f2e2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d2d1dd64-0850-4db4-aa50-97517000a4ce" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_4e5bb5ad-c936-4138-a71e-cf352774f2e2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_875e1c24-3bda-4bf0-bb82-a7b6789d8430" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d2d1dd64-0850-4db4-aa50-97517000a4ce" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_875e1c24-3bda-4bf0-bb82-a7b6789d8430" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_a21baa83-1f5a-44b6-adde-1761ba39cd33" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d2d1dd64-0850-4db4-aa50-97517000a4ce" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_a21baa83-1f5a-44b6-adde-1761ba39cd33" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_85453ea1-6d8a-406d-a078-a276c0923807" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d2d1dd64-0850-4db4-aa50-97517000a4ce" xlink:to="loc_us-gaap_LongTermDebt_85453ea1-6d8a-406d-a078-a276c0923807" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_100876f8-d667-43da-a7f0-62ac3f03b6c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d2d1dd64-0850-4db4-aa50-97517000a4ce" xlink:to="loc_us-gaap_LongTermDebtCurrent_100876f8-d667-43da-a7f0-62ac3f03b6c5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_2311415e-3d4e-4e95-b31d-24c27d1e187f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d2d1dd64-0850-4db4-aa50-97517000a4ce" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_2311415e-3d4e-4e95-b31d-24c27d1e187f" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/DebtNarrativeDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#DebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/DebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_5847647a-1e7d-4195-be09-7a01146b1a25" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_ae3ed0ef-f966-468e-a692-973acdb3c8e6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5847647a-1e7d-4195-be09-7a01146b1a25" xlink:to="loc_us-gaap_DebtInstrumentTable_ae3ed0ef-f966-468e-a692-973acdb3c8e6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_f0db5aad-a9fd-4a7b-9258-d714efa28ebb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ae3ed0ef-f966-468e-a692-973acdb3c8e6" xlink:to="loc_us-gaap_CreditFacilityAxis_f0db5aad-a9fd-4a7b-9258-d714efa28ebb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_f0db5aad-a9fd-4a7b-9258-d714efa28ebb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_f0db5aad-a9fd-4a7b-9258-d714efa28ebb" xlink:to="loc_us-gaap_CreditFacilityDomain_f0db5aad-a9fd-4a7b-9258-d714efa28ebb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_8ffaf4d3-81ba-4cc2-b694-47cf0b31bf62" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_f0db5aad-a9fd-4a7b-9258-d714efa28ebb" xlink:to="loc_us-gaap_CreditFacilityDomain_8ffaf4d3-81ba-4cc2-b694-47cf0b31bf62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_A400MillionCreditFacilityMember_f47d22dc-3a2f-4288-b8bf-7922cfc3ecee" xlink:href="swx-20250331.xsd#swx_A400MillionCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_8ffaf4d3-81ba-4cc2-b694-47cf0b31bf62" xlink:to="loc_swx_A400MillionCreditFacilityMember_f47d22dc-3a2f-4288-b8bf-7922cfc3ecee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_db99b376-4417-47ed-aa62-05f8c4de19f2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_8ffaf4d3-81ba-4cc2-b694-47cf0b31bf62" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_db99b376-4417-47ed-aa62-05f8c4de19f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiSecuredRevolvingCreditFacilityMember_2225383c-c014-4e8e-af73-ddad0dc48bed" xlink:href="swx-20250331.xsd#swx_CenturiSecuredRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_8ffaf4d3-81ba-4cc2-b694-47cf0b31bf62" xlink:to="loc_swx_CenturiSecuredRevolvingCreditFacilityMember_2225383c-c014-4e8e-af73-ddad0dc48bed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_A300MillionCreditFacilityMember_37d66bda-fc59-4baf-8cc8-8cf1e3158c3e" xlink:href="swx-20250331.xsd#swx_A300MillionCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_8ffaf4d3-81ba-4cc2-b694-47cf0b31bf62" xlink:to="loc_swx_A300MillionCreditFacilityMember_37d66bda-fc59-4baf-8cc8-8cf1e3158c3e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_41158f00-08e7-4d37-85ea-e7e05d41aa09" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ae3ed0ef-f966-468e-a692-973acdb3c8e6" xlink:to="loc_dei_LegalEntityAxis_41158f00-08e7-4d37-85ea-e7e05d41aa09" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_41158f00-08e7-4d37-85ea-e7e05d41aa09_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_41158f00-08e7-4d37-85ea-e7e05d41aa09" xlink:to="loc_dei_EntityDomain_41158f00-08e7-4d37-85ea-e7e05d41aa09_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a8c3ff3e-99ee-4376-a17a-a8a2838dbd52" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_41158f00-08e7-4d37-85ea-e7e05d41aa09" xlink:to="loc_dei_EntityDomain_a8c3ff3e-99ee-4376-a17a-a8a2838dbd52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_e2c6995e-d30a-4f8d-a529-21d2d23cda09" xlink:href="swx-20250331.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_a8c3ff3e-99ee-4376-a17a-a8a2838dbd52" xlink:to="loc_swx_SouthwestGasCorporationMember_e2c6995e-d30a-4f8d-a529-21d2d23cda09" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_edb796cd-eaa2-43d3-96f7-e541fe09fb8d" xlink:href="swx-20250331.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_a8c3ff3e-99ee-4376-a17a-a8a2838dbd52" xlink:to="loc_swx_CenturiGroupInc.Member_edb796cd-eaa2-43d3-96f7-e541fe09fb8d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_1b899f87-5118-4dbe-81b8-20350d93264e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ae3ed0ef-f966-468e-a692-973acdb3c8e6" xlink:to="loc_us-gaap_DebtInstrumentAxis_1b899f87-5118-4dbe-81b8-20350d93264e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_1b899f87-5118-4dbe-81b8-20350d93264e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_1b899f87-5118-4dbe-81b8-20350d93264e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_1b899f87-5118-4dbe-81b8-20350d93264e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_74111fca-f0ea-4904-acfe-f7fa94698158" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_1b899f87-5118-4dbe-81b8-20350d93264e" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_74111fca-f0ea-4904-acfe-f7fa94698158" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiSecuredTermLoanFacilityAndRevolvingCreditFacilityMember_e82471fd-ad26-4850-8260-f06cd8296bbd" xlink:href="swx-20250331.xsd#swx_CenturiSecuredTermLoanFacilityAndRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_74111fca-f0ea-4904-acfe-f7fa94698158" xlink:to="loc_swx_CenturiSecuredTermLoanFacilityAndRevolvingCreditFacilityMember_e82471fd-ad26-4850-8260-f06cd8296bbd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiSecuredTermLoanFacilityMember_3027aa29-80c3-4e41-b5eb-aa8d64148649" xlink:href="swx-20250331.xsd#swx_CenturiSecuredTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_74111fca-f0ea-4904-acfe-f7fa94698158" xlink:to="loc_swx_CenturiSecuredTermLoanFacilityMember_3027aa29-80c3-4e41-b5eb-aa8d64148649" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiTermLoanFacilityMember_d24678d2-0521-4070-814b-0e21d000f845" xlink:href="swx-20250331.xsd#swx_CenturiTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_74111fca-f0ea-4904-acfe-f7fa94698158" xlink:to="loc_swx_CenturiTermLoanFacilityMember_d24678d2-0521-4070-814b-0e21d000f845" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_TermLoanDueJuly2025Member_e2f7af7f-a181-4f51-a312-9f5d56079d89" xlink:href="swx-20250331.xsd#swx_TermLoanDueJuly2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_74111fca-f0ea-4904-acfe-f7fa94698158" xlink:to="loc_swx_TermLoanDueJuly2025Member_e2f7af7f-a181-4f51-a312-9f5d56079d89" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_51aba78d-b582-4693-87b3-eaeca03c26e8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ae3ed0ef-f966-468e-a692-973acdb3c8e6" xlink:to="loc_us-gaap_VariableRateAxis_51aba78d-b582-4693-87b3-eaeca03c26e8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_51aba78d-b582-4693-87b3-eaeca03c26e8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_51aba78d-b582-4693-87b3-eaeca03c26e8" xlink:to="loc_us-gaap_VariableRateDomain_51aba78d-b582-4693-87b3-eaeca03c26e8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_500c08d3-cd0c-4e3d-908d-93cc6a7cb309" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_51aba78d-b582-4693-87b3-eaeca03c26e8" xlink:to="loc_us-gaap_VariableRateDomain_500c08d3-cd0c-4e3d-908d-93cc6a7cb309" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_588dcc53-f8ee-43b0-a560-31f66bd71e7e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_500c08d3-cd0c-4e3d-908d-93cc6a7cb309" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_588dcc53-f8ee-43b0-a560-31f66bd71e7e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_da3fce42-fbe0-4d17-be80-e4e7a981947d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_500c08d3-cd0c-4e3d-908d-93cc6a7cb309" xlink:to="loc_us-gaap_BaseRateMember_da3fce42-fbe0-4d17-be80-e4e7a981947d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CORRAMember_fae7f3fe-14a4-4002-a571-4aaec88791e2" xlink:href="swx-20250331.xsd#swx_CORRAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_500c08d3-cd0c-4e3d-908d-93cc6a7cb309" xlink:to="loc_swx_CORRAMember_fae7f3fe-14a4-4002-a571-4aaec88791e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_ef4c113e-ea45-40a6-9e9e-5be17c266e48" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ae3ed0ef-f966-468e-a692-973acdb3c8e6" xlink:to="loc_srt_RangeAxis_ef4c113e-ea45-40a6-9e9e-5be17c266e48" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_ef4c113e-ea45-40a6-9e9e-5be17c266e48_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_ef4c113e-ea45-40a6-9e9e-5be17c266e48" xlink:to="loc_srt_RangeMember_ef4c113e-ea45-40a6-9e9e-5be17c266e48_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_f27ed2e1-bf69-4209-aacb-dcc68b3adf45" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_ef4c113e-ea45-40a6-9e9e-5be17c266e48" xlink:to="loc_srt_RangeMember_f27ed2e1-bf69-4209-aacb-dcc68b3adf45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_b33f2b34-7e36-492d-a8a1-730e3eae45d9" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f27ed2e1-bf69-4209-aacb-dcc68b3adf45" xlink:to="loc_srt_MinimumMember_b33f2b34-7e36-492d-a8a1-730e3eae45d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_0defeb0b-b71c-4956-a599-71cdc09bcecf" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f27ed2e1-bf69-4209-aacb-dcc68b3adf45" xlink:to="loc_srt_MaximumMember_0defeb0b-b71c-4956-a599-71cdc09bcecf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_8523cd99-8aa6-419c-95ee-f82356a0aa64" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ae3ed0ef-f966-468e-a692-973acdb3c8e6" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_8523cd99-8aa6-419c-95ee-f82356a0aa64" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_8523cd99-8aa6-419c-95ee-f82356a0aa64_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_8523cd99-8aa6-419c-95ee-f82356a0aa64" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_8523cd99-8aa6-419c-95ee-f82356a0aa64_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_3b8a4b0d-b051-4493-98bf-2214391d1538" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_8523cd99-8aa6-419c-95ee-f82356a0aa64" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_3b8a4b0d-b051-4493-98bf-2214391d1538" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_c9407beb-86c0-4a6b-97e4-b97ea98f2cee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_3b8a4b0d-b051-4493-98bf-2214391d1538" xlink:to="loc_us-gaap_LineOfCreditMember_c9407beb-86c0-4a6b-97e4-b97ea98f2cee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_78de9fcb-97bc-4391-ba64-f2ee2f5ebf8e" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_78de9fcb-97bc-4391-ba64-f2ee2f5ebf8e_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_e71732ca-0bfd-4f36-b1d2-5839583a4dde" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_a26574bf-c54f-498c-9371-efbb536f2d18" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_1b0ea262-ce32-4f80-9f9f-6a76c69efe80" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeAxis_ed195c74-6683-4248-b665-4875a82247ca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortTermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ae3ed0ef-f966-468e-a692-973acdb3c8e6" xlink:to="loc_us-gaap_ShortTermDebtTypeAxis_ed195c74-6683-4248-b665-4875a82247ca" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_ed195c74-6683-4248-b665-4875a82247ca_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_ed195c74-6683-4248-b665-4875a82247ca" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_ed195c74-6683-4248-b665-4875a82247ca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_1b98a5e5-e3c3-40c5-82f3-58993fd4b118" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_ed195c74-6683-4248-b665-4875a82247ca" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_1b98a5e5-e3c3-40c5-82f3-58993fd4b118" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_528a293d-74fd-42fb-ae8f-d2b3e3f401a2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_1b98a5e5-e3c3-40c5-82f3-58993fd4b118" xlink:to="loc_us-gaap_SecuredDebtMember_528a293d-74fd-42fb-ae8f-d2b3e3f401a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_d2a9407b-20c5-45e1-8ebe-b8cb51aa4a42" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5847647a-1e7d-4195-be09-7a01146b1a25" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_d2a9407b-20c5-45e1-8ebe-b8cb51aa4a42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_LineOfCreditFacilityAmountClassifiedAsLongTermDebt_3fb1d7ce-cda1-4d81-9eb1-cb929f20cc7e" xlink:href="swx-20250331.xsd#swx_LineOfCreditFacilityAmountClassifiedAsLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5847647a-1e7d-4195-be09-7a01146b1a25" xlink:to="loc_swx_LineOfCreditFacilityAmountClassifiedAsLongTermDebt_3fb1d7ce-cda1-4d81-9eb1-cb929f20cc7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_LineOfCreditFacilityWorkingCapitalPurposes_5ec9775d-9208-41a2-af63-1c9ec9de8170" xlink:href="swx-20250331.xsd#swx_LineOfCreditFacilityWorkingCapitalPurposes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5847647a-1e7d-4195-be09-7a01146b1a25" xlink:to="loc_swx_LineOfCreditFacilityWorkingCapitalPurposes_5ec9775d-9208-41a2-af63-1c9ec9de8170" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_a5abedac-889d-493c-b1bd-4be012acf0b3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5847647a-1e7d-4195-be09-7a01146b1a25" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_a5abedac-889d-493c-b1bd-4be012acf0b3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_44944032-b340-4240-9dce-240080d4cee2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5847647a-1e7d-4195-be09-7a01146b1a25" xlink:to="loc_us-gaap_LongTermDebt_44944032-b340-4240-9dce-240080d4cee2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCollateralAmount_3424e4a5-9c52-4a49-93be-e405c83045dc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentCollateralAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5847647a-1e7d-4195-be09-7a01146b1a25" xlink:to="loc_us-gaap_DebtInstrumentCollateralAmount_3424e4a5-9c52-4a49-93be-e405c83045dc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_e17c9a99-3f21-4bca-b888-2e4348b99e47" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5847647a-1e7d-4195-be09-7a01146b1a25" xlink:to="loc_us-gaap_LineOfCredit_e17c9a99-3f21-4bca-b888-2e4348b99e47" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_LineOfCreditFacilityMaximumCommitmentAmount_30573196-3884-434a-a1c3-c0ab8f7591b4" xlink:href="swx-20250331.xsd#swx_LineOfCreditFacilityMaximumCommitmentAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5847647a-1e7d-4195-be09-7a01146b1a25" xlink:to="loc_swx_LineOfCreditFacilityMaximumCommitmentAmount_30573196-3884-434a-a1c3-c0ab8f7591b4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowings_fa664467-a16a-4019-a85e-e84f284f17ae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortTermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5847647a-1e7d-4195-be09-7a01146b1a25" xlink:to="loc_us-gaap_ShortTermBorrowings_fa664467-a16a-4019-a85e-e84f284f17ae" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_4e50fa44-98e7-4fc3-b9b6-b200bc52b2f2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5847647a-1e7d-4195-be09-7a01146b1a25" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_4e50fa44-98e7-4fc3-b9b6-b200bc52b2f2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_73d97ed9-9121-4ad3-8f46-3e9f84b94665" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_5847647a-1e7d-4195-be09-7a01146b1a25" xlink:to="loc_us-gaap_LongTermDebtCurrent_73d97ed9-9121-4ad3-8f46-3e9f84b94665" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/SegmentInformationNarrativeDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#SegmentInformationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/SegmentInformationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_5659da8f-1893-4806-9e98-f2c1244cfbdc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_0c7b910a-5667-4d47-b985-66c514506f30" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_5659da8f-1893-4806-9e98-f2c1244cfbdc" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_0c7b910a-5667-4d47-b985-66c514506f30" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_ca271e64-ecc0-4ac3-aaf1-6b5ab2049bd3" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_0c7b910a-5667-4d47-b985-66c514506f30" xlink:to="loc_srt_StatementGeographicalAxis_ca271e64-ecc0-4ac3-aaf1-6b5ab2049bd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_ca271e64-ecc0-4ac3-aaf1-6b5ab2049bd3_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_ca271e64-ecc0-4ac3-aaf1-6b5ab2049bd3" xlink:to="loc_srt_SegmentGeographicalDomain_ca271e64-ecc0-4ac3-aaf1-6b5ab2049bd3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_77201a66-43ff-4c70-a07b-0c13fe59067f" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_ca271e64-ecc0-4ac3-aaf1-6b5ab2049bd3" xlink:to="loc_srt_SegmentGeographicalDomain_77201a66-43ff-4c70-a07b-0c13fe59067f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_cb19e0b2-a828-4664-8155-37b5dace717d" xlink:href="https://xbrl.sec.gov/country/2024/country-2024.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_77201a66-43ff-4c70-a07b-0c13fe59067f" xlink:to="loc_country_US_cb19e0b2-a828-4664-8155-37b5dace717d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_a9e3e38c-4b03-43a4-a8a3-fce3d4faae9f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_0c7b910a-5667-4d47-b985-66c514506f30" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_a9e3e38c-4b03-43a4-a8a3-fce3d4faae9f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_a9e3e38c-4b03-43a4-a8a3-fce3d4faae9f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_a9e3e38c-4b03-43a4-a8a3-fce3d4faae9f" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_a9e3e38c-4b03-43a4-a8a3-fce3d4faae9f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_27ea9c2b-442d-41a8-86a6-785ab217a1d2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_a9e3e38c-4b03-43a4-a8a3-fce3d4faae9f" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_27ea9c2b-442d-41a8-86a6-785ab217a1d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetAssetsGeographicAreaMember_077d682c-4e6c-4cd2-8ae7-99eedbbeb60e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetAssetsGeographicAreaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_27ea9c2b-442d-41a8-86a6-785ab217a1d2" xlink:to="loc_us-gaap_NetAssetsGeographicAreaMember_077d682c-4e6c-4cd2-8ae7-99eedbbeb60e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_9c3622c7-91cb-4a78-a7fe-62513fb6cd1b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_0c7b910a-5667-4d47-b985-66c514506f30" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_9c3622c7-91cb-4a78-a7fe-62513fb6cd1b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_9c3622c7-91cb-4a78-a7fe-62513fb6cd1b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_9c3622c7-91cb-4a78-a7fe-62513fb6cd1b" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_9c3622c7-91cb-4a78-a7fe-62513fb6cd1b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_4a5b0278-663f-4108-a439-6abd916424c4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_9c3622c7-91cb-4a78-a7fe-62513fb6cd1b" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_4a5b0278-663f-4108-a439-6abd916424c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicConcentrationRiskMember_12539506-a120-49b3-ae6b-15807ea88bac" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GeographicConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_4a5b0278-663f-4108-a439-6abd916424c4" xlink:to="loc_us-gaap_GeographicConcentrationRiskMember_12539506-a120-49b3-ae6b-15807ea88bac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_2110352f-ab61-4964-adf1-2dfd0c1dd70f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_5659da8f-1893-4806-9e98-f2c1244cfbdc" xlink:to="loc_us-gaap_NumberOfReportableSegments_2110352f-ab61-4964-adf1-2dfd0c1dd70f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_a49b504a-09ae-4d48-9705-2e0661222df4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_5659da8f-1893-4806-9e98-f2c1244cfbdc" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_a49b504a-09ae-4d48-9705-2e0661222df4" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/SegmentInformationScheduleofAccountsReceivableNotEliminatedDuringConsolidationDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#SegmentInformationScheduleofAccountsReceivableNotEliminatedDuringConsolidationDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/SegmentInformationScheduleofAccountsReceivableNotEliminatedDuringConsolidationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_340dccf1-5c30-44d1-8ff4-9247ca269a5a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d9ced-4a8c-4583-94ab-0fb93d056640" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_340dccf1-5c30-44d1-8ff4-9247ca269a5a" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d9ced-4a8c-4583-94ab-0fb93d056640" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_07c768ad-49c2-4de4-86d5-0dc0e67fa4a8" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d9ced-4a8c-4583-94ab-0fb93d056640" xlink:to="loc_dei_LegalEntityAxis_07c768ad-49c2-4de4-86d5-0dc0e67fa4a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_07c768ad-49c2-4de4-86d5-0dc0e67fa4a8_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_07c768ad-49c2-4de4-86d5-0dc0e67fa4a8" xlink:to="loc_dei_EntityDomain_07c768ad-49c2-4de4-86d5-0dc0e67fa4a8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_61ba3085-fbfe-402b-9f2a-bd292e4cf58c" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_07c768ad-49c2-4de4-86d5-0dc0e67fa4a8" xlink:to="loc_dei_EntityDomain_61ba3085-fbfe-402b-9f2a-bd292e4cf58c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_69851b2e-4c50-4bab-b641-2068ccf26acd" xlink:href="swx-20250331.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_61ba3085-fbfe-402b-9f2a-bd292e4cf58c" xlink:to="loc_swx_CenturiGroupInc.Member_69851b2e-4c50-4bab-b641-2068ccf26acd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_7f0e8313-4b69-4529-a27e-443f517085d2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_019d9ced-4a8c-4583-94ab-0fb93d056640" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_7f0e8313-4b69-4529-a27e-443f517085d2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_7f0e8313-4b69-4529-a27e-443f517085d2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_7f0e8313-4b69-4529-a27e-443f517085d2" xlink:to="loc_us-gaap_RelatedPartyDomain_7f0e8313-4b69-4529-a27e-443f517085d2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_e388e19a-29fe-461d-8a6f-fda553b0b07b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_7f0e8313-4b69-4529-a27e-443f517085d2" xlink:to="loc_us-gaap_RelatedPartyDomain_e388e19a-29fe-461d-8a6f-fda553b0b07b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_3e5e7114-b433-49e7-b885-87939caa44bb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_e388e19a-29fe-461d-8a6f-fda553b0b07b" xlink:to="loc_us-gaap_RelatedPartyMember_3e5e7114-b433-49e7-b885-87939caa44bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_98c9a6cb-f8cc-4cb3-a381-6f0e69f1bf9b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_340dccf1-5c30-44d1-8ff4-9247ca269a5a" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_98c9a6cb-f8cc-4cb3-a381-6f0e69f1bf9b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/SegmentInformationScheduleofRevenuesbyGeographicAreaDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#SegmentInformationScheduleofRevenuesbyGeographicAreaDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/SegmentInformationScheduleofRevenuesbyGeographicAreaDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_79339e41-c413-42b6-9454-6dfddca11fbf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_62773a73-aaea-45ec-ae34-7af08b862e91" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_79339e41-c413-42b6-9454-6dfddca11fbf" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_62773a73-aaea-45ec-ae34-7af08b862e91" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_7d68ac3b-885a-4411-8e2c-de3d7f619634" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_62773a73-aaea-45ec-ae34-7af08b862e91" xlink:to="loc_srt_StatementGeographicalAxis_7d68ac3b-885a-4411-8e2c-de3d7f619634" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_7d68ac3b-885a-4411-8e2c-de3d7f619634_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_7d68ac3b-885a-4411-8e2c-de3d7f619634" xlink:to="loc_srt_SegmentGeographicalDomain_7d68ac3b-885a-4411-8e2c-de3d7f619634_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_1d43b62d-de25-49db-8f95-3f49501dd3aa" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_7d68ac3b-885a-4411-8e2c-de3d7f619634" xlink:to="loc_srt_SegmentGeographicalDomain_1d43b62d-de25-49db-8f95-3f49501dd3aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_f7477d5f-dab6-4ec2-9d76-442496130e84" xlink:href="https://xbrl.sec.gov/country/2024/country-2024.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_1d43b62d-de25-49db-8f95-3f49501dd3aa" xlink:to="loc_country_US_f7477d5f-dab6-4ec2-9d76-442496130e84" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CA_7fb8d9d7-8af9-4c6e-badc-f3e5ffa1b1f8" xlink:href="https://xbrl.sec.gov/country/2024/country-2024.xsd#country_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_1d43b62d-de25-49db-8f95-3f49501dd3aa" xlink:to="loc_country_CA_7fb8d9d7-8af9-4c6e-badc-f3e5ffa1b1f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatedAndUnregulatedOperatingRevenue_4e8301ca-8876-4825-b9e6-200792b08b30" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RegulatedAndUnregulatedOperatingRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_79339e41-c413-42b6-9454-6dfddca11fbf" xlink:to="loc_us-gaap_RegulatedAndUnregulatedOperatingRevenue_4e8301ca-8876-4825-b9e6-200792b08b30" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/SegmentInformationScheduleofSegmentReportingInformationDetails" xlink:type="simple" xlink:href="swx-20250331.xsd#SegmentInformationScheduleofSegmentReportingInformationDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/SegmentInformationScheduleofSegmentReportingInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_2bc7f7f8-f84c-402e-89f5-d98c7466e9c7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_2bc7f7f8-f84c-402e-89f5-d98c7466e9c7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_46327de1-d388-4bcb-baab-acb6d2ae45de" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_2bc7f7f8-f84c-402e-89f5-d98c7466e9c7" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_46327de1-d388-4bcb-baab-acb6d2ae45de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_46327de1-d388-4bcb-baab-acb6d2ae45de_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_46327de1-d388-4bcb-baab-acb6d2ae45de" xlink:to="loc_us-gaap_SegmentDomain_46327de1-d388-4bcb-baab-acb6d2ae45de_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_8c3e59ad-9509-4a18-b45b-9fe71f14151e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_46327de1-d388-4bcb-baab-acb6d2ae45de" xlink:to="loc_us-gaap_SegmentDomain_8c3e59ad-9509-4a18-b45b-9fe71f14151e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_NaturalGasDistributionSegmentMember_d2783ebe-284c-4181-897e-b70a1d6cf2f1" xlink:href="swx-20250331.xsd#swx_NaturalGasDistributionSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8c3e59ad-9509-4a18-b45b-9fe71f14151e" xlink:to="loc_swx_NaturalGasDistributionSegmentMember_d2783ebe-284c-4181-897e-b70a1d6cf2f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_UtilityInfrastructureServicesSegmentMember_a960beef-5f5a-461f-bfd5-8135a5a87ce2" xlink:href="swx-20250331.xsd#swx_UtilityInfrastructureServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8c3e59ad-9509-4a18-b45b-9fe71f14151e" xlink:to="loc_swx_UtilityInfrastructureServicesSegmentMember_a960beef-5f5a-461f-bfd5-8135a5a87ce2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_1a4775f5-ef51-4ad0-a422-1c64163268bc" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_2bc7f7f8-f84c-402e-89f5-d98c7466e9c7" xlink:to="loc_srt_ConsolidationItemsAxis_1a4775f5-ef51-4ad0-a422-1c64163268bc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_1a4775f5-ef51-4ad0-a422-1c64163268bc_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_1a4775f5-ef51-4ad0-a422-1c64163268bc" xlink:to="loc_srt_ConsolidationItemsDomain_1a4775f5-ef51-4ad0-a422-1c64163268bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_c091ef51-e7be-4b11-86e9-6bab7db76bd5" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_1a4775f5-ef51-4ad0-a422-1c64163268bc" xlink:to="loc_srt_ConsolidationItemsDomain_c091ef51-e7be-4b11-86e9-6bab7db76bd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OperatingSegmentsExcludingIntersegmentEliminationMember_188f049f-124b-4846-9cd0-5b9e17270c79" xlink:href="swx-20250331.xsd#swx_OperatingSegmentsExcludingIntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_c091ef51-e7be-4b11-86e9-6bab7db76bd5" xlink:to="loc_swx_OperatingSegmentsExcludingIntersegmentEliminationMember_188f049f-124b-4846-9cd0-5b9e17270c79" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_e935d215-4d47-4fb1-b312-a81bfdb9e589" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_c091ef51-e7be-4b11-86e9-6bab7db76bd5" xlink:to="loc_us-gaap_OperatingSegmentsMember_e935d215-4d47-4fb1-b312-a81bfdb9e589" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_c153a5f9-2e10-4f78-b4a4-cb5b46c0429d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_c091ef51-e7be-4b11-86e9-6bab7db76bd5" xlink:to="loc_us-gaap_IntersegmentEliminationMember_c153a5f9-2e10-4f78-b4a4-cb5b46c0429d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_a3feef90-c0d4-4b01-819a-197ac58bc99f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MaterialReconcilingItemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_c091ef51-e7be-4b11-86e9-6bab7db76bd5" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_a3feef90-c0d4-4b01-819a-197ac58bc99f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatedAndUnregulatedOperatingRevenue_d4b3ec7f-8710-4126-b034-dd9a9c8f15b1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RegulatedAndUnregulatedOperatingRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_RegulatedAndUnregulatedOperatingRevenue_d4b3ec7f-8710-4126-b034-dd9a9c8f15b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseGasAndPetroleumPurchased_23093f43-b7af-41c6-84ea-272ba18189d1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UtilitiesOperatingExpenseGasAndPetroleumPurchased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseGasAndPetroleumPurchased_23093f43-b7af-41c6-84ea-272ba18189d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_40779037-b47d-4f74-a2bc-a697bb541050" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_40779037-b47d-4f74-a2bc-a697bb541050" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_47ca9195-e38a-4d0a-adea-04f9ab96d7a3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_47ca9195-e38a-4d0a-adea-04f9ab96d7a3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_75a5cab9-ae3b-460d-b55f-05a82a492b47" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_75a5cab9-ae3b-460d-b55f-05a82a492b47" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_409587e6-5503-4c8f-bfe4-807f5c03e2e1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_409587e6-5503-4c8f-bfe4-807f5c03e2e1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_67a95188-8241-47ff-9820-e6b8ee4fa04f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_67a95188-8241-47ff-9820-e6b8ee4fa04f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_f326458d-8c7a-4526-b1ad-93a9b78c367a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_ProfitLoss_f326458d-8c7a-4526-b1ad-93a9b78c367a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_08118480-a90a-4cd9-ae49-4c93dbc2a040" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_08118480-a90a-4cd9-ae49-4c93dbc2a040" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_d98183b2-3e01-4b62-bd3c-825b68432485" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_NetIncomeLoss_d98183b2-3e01-4b62-bd3c-825b68432485" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeOther_4fc4de5f-538e-4f6e-9364-c2795be6c568" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestIncomeOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_InterestIncomeOther_4fc4de5f-538e-4f6e-9364-c2795be6c568" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_28bd8e25-8703-44e9-8b99-73816c610698" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_InterestExpenseNonoperating_28bd8e25-8703-44e9-8b99-73816c610698" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_35ab097d-077e-4348-8245-c40c355adba2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_DepreciationAndAmortization_35ab097d-077e-4348-8245-c40c355adba2" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_bd35a787-18be-4105-8c5c-7347a7dc1e6b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_Assets_bd35a787-18be-4105-8c5c-7347a7dc1e6b" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_fe20d226-df04-4630-93dd-01351a771529" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SegmentExpenditureAdditionToLongLivedAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_a20cd06d-5534-49d3-b18c-21dc1febadee" xlink:to="loc_us-gaap_SegmentExpenditureAdditionToLongLivedAssets_fe20d226-df04-4630-93dd-01351a771529" xlink:type="arc" order="14"/>
  </link:definitionLink>
</link:linkbase>
