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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2022-05-06</periodOfReport>

    <dateOfOriginalSubmission>2022-05-10</dateOfOriginalSubmission>

    <issuer>
        <issuerCik>0001825480</issuerCik>
        <issuerName>Poshmark, Inc.</issuerName>
        <issuerTradingSymbol>POSH</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001876966</rptOwnerCik>
            <rptOwnerName>BECKWITH EBONY</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O POSHMARK INC.</rptOwnerStreet1>
            <rptOwnerStreet2>203 REDWOOD SHORES PARKWAY</rptOwnerStreet2>
            <rptOwnerCity>REDWOOD CITY</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94065</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2022-05-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>614</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4451</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>35.01</value>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2022-05-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1456</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2031-08-06</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1456</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10195</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Each share is represented by a restricted stock unit (&quot;RSU&quot;). Each RSU represents a contingent right to receive one share of the Issuer's Class A Common Stock upon settlement. The RSUs will vest in 3 equal installments on September 1, 2022, September 1, 2023 and September 1, 2024, subject to the Reporting Person's continued service through the applicable vesting date. Vested shares will be deferred in accordance with the Reporting Person's deferral election pursuant to the Rules and Conditions for the Poshmark, Inc. Non-Employee Directors' Deferred Compensation Program. The number of RSUs granted have been adjusted from the original filing due to a miscalculation of the RSUs granted.</footnote>
        <footnote id="F2">The exercise price has been adjusted from the original filing due to a miscalculation of the exercise price.</footnote>
        <footnote id="F3">The stock options granted have been adjusted from the original filing due to a miscalculation of the number of stock options granted.</footnote>
        <footnote id="F4">The options will vest and become exercisable in 3 equal installments on September 1, 2022, September 1, 2023, and September 1, 2024, subject to the Reporting Person's continued board service to the Issuer through each such vesting date.</footnote>
    </footnotes>

    <remarks>We are amending this Form 4 to correct an administrative error in the total number of stock options and RSUs granted to the Reporting Person. We are also amending the exercise price of the stock options from the original filing due to a miscalculation of the exercise price. Finally, we have moved the RSUs from Table II in the original filing to Table I because the RSUs are deemed to be an acquisition of the underlying Class A Common Stock.</remarks>

    <ownerSignature>
        <signatureName>/s/ Evan Ferl, Attorney-in-Fact</signatureName>
        <signatureDate>2022-05-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
