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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2016-06-15</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001586105</issuerCik>
        <issuerName>Egalet Corp</issuerName>
        <issuerTradingSymbol>EGLT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001591113</rptOwnerCik>
            <rptOwnerName>Radie Robert S</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1301 JOY RUN</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>GLENMOORE</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19343</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President and CEO</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Common Stock (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>8.59</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-06-15</value>
                <footnoteId id="F1"/>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>265000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>8.59</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2025-11-20</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>265000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>265000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The grant was approved by the Compensation Committee of Egalet Corporation's board of directors on November 20, 2015, subject to stockholder approval of an increase in the number of shares available for issuance under the Egalet Corporation 2013 Stock-Based Incentive Compensation Plan, pursuant to which the grant was made. Egalet Corporation's stockholders approved the increase on June 15, 2016.</footnote>
        <footnote id="F2">These options to purchase shares of common stock vest with respect to 25% of the shares on November 20, 2016 and for 1/48 of the shares set forth above each month thereafter until the option is 100% vested, subject to the filing person's continued employment.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Stan Musial, attorney in fact for Robert Radie</signatureName>
        <signatureDate>2016-06-17</signatureDate>
    </ownerSignature>
</ownershipDocument>
