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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019db6cd-6939-73f0-8b9d-deaa2b9a9c49,g:72b69829-04f3-4bd3-adc1-9545d2a02bc0-->
<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.unitedcontinentalholdings.com/role/DocumentandEntityInformation" xlink:type="simple" xlink:href="ual-20260715.xsd#DocumentandEntityInformation"/>
  <link:definitionLink xlink:role="http://www.unitedcontinentalholdings.com/role/DocumentandEntityInformation" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_019db6cd-693a-7065-bccf-cbd828b17534" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_EntitiesTable_019db6cd-693a-7065-bccf-cbd828b17534" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019db6cd-693a-78d8-88e2-3d4967c97263" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019db6cd-693a-7065-bccf-cbd828b17534" xlink:to="loc_dei_LegalEntityAxis_019db6cd-693a-78d8-88e2-3d4967c97263" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019db6cd-693a-78d8-88e2-3d4967c97263_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019db6cd-693a-78d8-88e2-3d4967c97263" xlink:to="loc_dei_EntityDomain_019db6cd-693a-78d8-88e2-3d4967c97263_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019db6cd-693a-70cd-a9a7-12969daf0092" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019db6cd-693a-78d8-88e2-3d4967c97263" xlink:to="loc_dei_EntityDomain_019db6cd-693a-70cd-a9a7-12969daf0092" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ual_UnitedAirLinesIncMember_019db6cd-693a-72da-b488-015679e151ea" xlink:href="ual-20260715.xsd#ual_UnitedAirLinesIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019db6cd-693a-70cd-a9a7-12969daf0092" xlink:to="loc_ual_UnitedAirLinesIncMember_019db6cd-693a-72da-b488-015679e151ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019db6cd-693a-7d81-9aad-9a943a74b447" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_019db6cd-693a-7065-bccf-cbd828b17534" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019db6cd-693a-7d81-9aad-9a943a74b447" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019db6cd-693a-7d81-9aad-9a943a74b447_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019db6cd-693a-7d81-9aad-9a943a74b447" xlink:to="loc_us-gaap_ClassOfStockDomain_019db6cd-693a-7d81-9aad-9a943a74b447_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019db6cd-693a-7721-a395-28387885e7bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019db6cd-693a-7d81-9aad-9a943a74b447" xlink:to="loc_us-gaap_ClassOfStockDomain_019db6cd-693a-7721-a395-28387885e7bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019db6cd-693a-7082-a655-a5f6b857f84f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019db6cd-693a-7721-a395-28387885e7bd" xlink:to="loc_us-gaap_WarrantMember_019db6cd-693a-7082-a655-a5f6b857f84f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019db6cd-693a-74b7-b897-c1698fb091ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019db6cd-693a-7721-a395-28387885e7bd" xlink:to="loc_us-gaap_CommonStockMember_019db6cd-693a-74b7-b897-c1698fb091ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019db6cd-693a-704f-89c9-dcadc74a89a0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_DocumentType_019db6cd-693a-704f-89c9-dcadc74a89a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019db6cd-693a-7460-9ff7-94c2162c5464" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_AmendmentFlag_019db6cd-693a-7460-9ff7-94c2162c5464" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019db6cd-693a-729c-b201-5813ada18f4c" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_DocumentPeriodEndDate_019db6cd-693a-729c-b201-5813ada18f4c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019db6cd-693a-7b4f-a48f-52bfe256207d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_EntityRegistrantName_019db6cd-693a-7b4f-a48f-52bfe256207d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019db6cd-693a-7a4d-bc7a-d9caabf8d167" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_EntityCentralIndexKey_019db6cd-693a-7a4d-bc7a-d9caabf8d167" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019db6cd-693a-70f0-9d31-085b8a476130" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019db6cd-693a-70f0-9d31-085b8a476130" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019db6cd-693a-7a34-bb42-5666951e483b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_EntityFileNumber_019db6cd-693a-7a34-bb42-5666951e483b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019db6cd-693a-7ec8-892e-9e6b87d27d45" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_EntityAddressAddressLine1_019db6cd-693a-7ec8-892e-9e6b87d27d45" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019db6cd-693a-742e-b466-a2be90388580" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_EntityAddressCityOrTown_019db6cd-693a-742e-b466-a2be90388580" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019db6cd-693a-76b2-b0b4-33a54ac7d058" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_EntityAddressStateOrProvince_019db6cd-693a-76b2-b0b4-33a54ac7d058" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019db6cd-693a-7f76-a4eb-ebb52a1ff2d4" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_EntityAddressPostalZipCode_019db6cd-693a-7f76-a4eb-ebb52a1ff2d4" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019db6cd-693a-7da5-8ddb-980f48d78b53" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_CityAreaCode_019db6cd-693a-7da5-8ddb-980f48d78b53" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019db6cd-693a-769c-9ffb-736e1c736ac9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_LocalPhoneNumber_019db6cd-693a-769c-9ffb-736e1c736ac9" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_019db6cd-693a-7851-91bc-30aad396c4ee" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_WrittenCommunications_019db6cd-693a-7851-91bc-30aad396c4ee" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_019db6cd-693a-7616-847a-c02fdd96a3c2" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_SolicitingMaterial_019db6cd-693a-7616-847a-c02fdd96a3c2" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_019db6cd-693a-71ba-995b-8c17637f368c" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_PreCommencementTenderOffer_019db6cd-693a-71ba-995b-8c17637f368c" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_019db6cd-693a-736d-88e1-e4f43df8ceb6" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_019db6cd-693a-736d-88e1-e4f43df8ceb6" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019db6cd-693a-77f5-8b53-9a54c5b21e77" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_Security12bTitle_019db6cd-693a-77f5-8b53-9a54c5b21e77" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019db6cd-693a-76b8-b35f-2bbd9e8e377d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_SecurityExchangeName_019db6cd-693a-76b8-b35f-2bbd9e8e377d" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019db6cd-693a-7b9b-bc6d-f0106f9e8b0d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_EntityEmergingGrowthCompany_019db6cd-693a-7b9b-bc6d-f0106f9e8b0d" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_NoTradingSymbolFlag_019db6cd-693a-7f9c-8e9c-53b26ea31893" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_NoTradingSymbolFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_NoTradingSymbolFlag_019db6cd-693a-7f9c-8e9c-53b26ea31893" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019db6cd-693a-771f-8c25-a0ad83ccd712" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_TradingSymbol_019db6cd-693a-771f-8c25-a0ad83ccd712" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019db6cd-693a-71cc-ae47-04c4cdd8042d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_019db6cd-693a-7e97-8ada-ce74f825c72a" xlink:to="loc_dei_EntityTaxIdentificationNumber_019db6cd-693a-71cc-ae47-04c4cdd8042d" xlink:type="arc" order="22"/>
  </link:definitionLink>
</link:linkbase>
