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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019c202d-cda4-7133-be2c-34b4ce98eddb,g:072bff9b-9c06-4e9c-b686-e854a6e4ee49-->
<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.suncountry.com/role/Cover" xlink:type="simple" xlink:href="sncy-20260205.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.suncountry.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019c202d-cda4-7278-9225-f6435e80021e" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019c202d-cda4-707b-80c5-62b5d058b7f3" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_EntitiesTable_019c202d-cda4-707b-80c5-62b5d058b7f3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityListingsExchangeAxis_019c202d-cda4-79c5-9de5-5fdbbc4810c2" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityListingsExchangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019c202d-cda4-707b-80c5-62b5d058b7f3" xlink:to="loc_dei_EntityListingsExchangeAxis_019c202d-cda4-79c5-9de5-5fdbbc4810c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_ExchangeDomain_019c202d-cda4-79c5-9de5-5fdbbc4810c2_default" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_ExchangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_EntityListingsExchangeAxis_019c202d-cda4-79c5-9de5-5fdbbc4810c2" xlink:to="loc_dei_ExchangeDomain_019c202d-cda4-79c5-9de5-5fdbbc4810c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_ExchangeDomain_019c202d-cda4-7cee-9cde-3468f3e860e7" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_ExchangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_EntityListingsExchangeAxis_019c202d-cda4-79c5-9de5-5fdbbc4810c2" xlink:to="loc_dei_ExchangeDomain_019c202d-cda4-7cee-9cde-3468f3e860e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncy_TheNasdaqStockMarketLLCMember_019c202d-cda4-702f-b9fa-87e9735c96aa" xlink:href="sncy-20260205.xsd#sncy_TheNasdaqStockMarketLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_ExchangeDomain_019c202d-cda4-7cee-9cde-3468f3e860e7" xlink:to="loc_sncy_TheNasdaqStockMarketLLCMember_019c202d-cda4-702f-b9fa-87e9735c96aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019c202d-cda4-70b2-84ab-119ecb3324d4" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_DocumentType_019c202d-cda4-70b2-84ab-119ecb3324d4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019c202d-cda4-730f-9121-edd498b1ffaf" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_DocumentPeriodEndDate_019c202d-cda4-730f-9121-edd498b1ffaf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019c202d-cda4-7b0b-8538-00ac83916edb" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_EntityRegistrantName_019c202d-cda4-7b0b-8538-00ac83916edb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019c202d-cda4-7e58-8891-8393fc5603d6" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019c202d-cda4-7e58-8891-8393fc5603d6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019c202d-cda4-7757-bc3f-38ba61c35353" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_EntityFileNumber_019c202d-cda4-7757-bc3f-38ba61c35353" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019c202d-cda4-71d0-8ea7-1e0700fa28ae" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_EntityTaxIdentificationNumber_019c202d-cda4-71d0-8ea7-1e0700fa28ae" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019c202d-cda4-7588-b41c-6d10e25b5074" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_EntityAddressAddressLine1_019c202d-cda4-7588-b41c-6d10e25b5074" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019c202d-cda4-781d-8609-a68dccd076ae" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_EntityAddressCityOrTown_019c202d-cda4-781d-8609-a68dccd076ae" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019c202d-cda4-7ba6-81a7-95e3147e1ecd" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_EntityAddressStateOrProvince_019c202d-cda4-7ba6-81a7-95e3147e1ecd" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019c202d-cda4-7d23-846f-9a6fce05615f" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_EntityAddressPostalZipCode_019c202d-cda4-7d23-846f-9a6fce05615f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019c202d-cda4-722a-8df3-e226c4ec8565" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_CityAreaCode_019c202d-cda4-722a-8df3-e226c4ec8565" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019c202d-cda4-7167-950e-71bd7aa9fbfa" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_LocalPhoneNumber_019c202d-cda4-7167-950e-71bd7aa9fbfa" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_019c202d-cda4-7254-9240-b7464ea3a3b2" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_WrittenCommunications_019c202d-cda4-7254-9240-b7464ea3a3b2" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_019c202d-cda4-736f-b8f7-f9571cd085b3" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_SolicitingMaterial_019c202d-cda4-736f-b8f7-f9571cd085b3" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_019c202d-cda4-7ee5-a146-b89d8f4125a4" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_PreCommencementTenderOffer_019c202d-cda4-7ee5-a146-b89d8f4125a4" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_019c202d-cda4-7076-841c-16cf0780210b" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_019c202d-cda4-7076-841c-16cf0780210b" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019c202d-cda4-7383-8e96-3d91c1959ce3" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_Security12bTitle_019c202d-cda4-7383-8e96-3d91c1959ce3" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019c202d-cda4-77e4-912b-bc8885b7aa46" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_TradingSymbol_019c202d-cda4-77e4-912b-bc8885b7aa46" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019c202d-cda4-7366-9c9d-00152f3cb778" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_SecurityExchangeName_019c202d-cda4-7366-9c9d-00152f3cb778" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019c202d-cda4-7564-baf1-0ef7062a2e1f" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_EntityEmergingGrowthCompany_019c202d-cda4-7564-baf1-0ef7062a2e1f" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019c202d-cda4-7937-8d2a-021307151786" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_EntityCentralIndexKey_019c202d-cda4-7937-8d2a-021307151786" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019c202d-cda4-75d6-84f7-efd6af3600c7" 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_019c202d-cda4-7278-9225-f6435e80021e" xlink:to="loc_dei_AmendmentFlag_019c202d-cda4-75d6-84f7-efd6af3600c7" xlink:type="arc" order="21"/>
  </link:definitionLink>
</link:linkbase>
