<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2017-07-31</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001698990</issuerCik>
        <issuerName>Magnolia Oil &amp; Gas Corp</issuerName>
        <issuerTradingSymbol>MGY</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001704120</rptOwnerCik>
            <rptOwnerName>Davidson Martin</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O TPG GLOBAL, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>301 COMMERCE STREET, SUITE 3300</rptOwnerStreet2>
            <rptOwnerCity>FORT WORTH</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>76102</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Former Officer</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
            </securityTitle>
            <transactionDate>
                <value>2018-07-31</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>5000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>10.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Martin Davidson is a TPG Partner. TPG is affiliated with TPG Pace Energy Sponsor, LLC, which directly holds an aggregate of 16,090,000 shares of Class A Common Stock, par value $0.0001 per share, of Magnolia Oil &amp; Gas Corporation (the &quot;Issuer&quot;).</footnote>
        <footnote id="F2">Mr. Davidson disclaims beneficial ownership of all of the securities that are or may be beneficially owned by TPG Pace Energy Sponsor, LLC or any of its affiliates. Pursuant to Rule 16a-1(a)(4) under the Securities Exchange Act of 1934, as amended (the &quot;Exchange Act&quot;), this filing shall not be deemed an admission that Mr. Davidson is, for purposes of Section 16 of the Exchange Act or otherwise, the beneficial owner of any equity securities of the Issuer for purposes of Section 16 of the Exchange Act or otherwise.</footnote>
    </footnotes>

    <remarks>(3) Michael LaGatta is signing on behalf of Mr. Davidson pursuant to the authorization and designation letter dated April 28, 2017, which was previously filed with the Securities and Exchange Commission.</remarks>

    <ownerSignature>
        <signatureName>/s/ Michael LaGatta on behalf of Martin Davidson (3)</signatureName>
        <signatureDate>2018-08-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
