UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No. )

Filed by the Registrant x          Filed by a Party other than the Registrant ¨

Check the appropriate box:

¨ Preliminary Proxy Statement

¨ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)

¨ Definitive Proxy Statement

x Definitive Additional Materials

¨ Soliciting Material under §240.14a-12

SQUARESPACE, INC.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

x No fee required.

¨ Fee paid previously with preliminary materials.

¨ Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a6(i)(1) and 0-11

Your Vote Counts! SQUARESPACE, INC. 225 VARICK STREET, 12TH FLOOR NEW YORK, NEW YORK 10014 SQUARESPACE, INC. 2022 Annual Meeting Vote by June 1, 2022 11:59 PM ET You invested in SQUARESPACE, INC. and it’s time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy material for the stockholder meeting to be held on June 2, 2022. Vote Virtually at the Meeting* June 2, 2022 12:00 PM EDT Virtually at: www.virtualshareholdermeeting.com/SQSP2022 *Please check the meeting materials for any special requirements for meeting attendance. Smartphone users Point your camera here and vote without entering a control number V1.1 For complete information and to vote, visit www.ProxyVote.com Control # D79354-P68606 Get informed before you vote View the Notice and Proxy Statement and Annual Report online OR you can receive a free paper or email copy of the material(s) by requesting prior to May 19, 2022. If you would like to request a copy of the material(s) for this and/or future stockholder meetings, you may (1) visit www.ProxyVote.com, (2) call 1-800-579-1639 or (3) send an email to sendmaterial@proxyvote.com. If sending an email, please include your control number (indicated below) in the subject line. Unless requested, you will not otherwise receive a paper or email copy.

THIS IS NOT A VOTABLE BALLOT This is an overview of the proposals being presented at the upcoming stockholder meeting. Please follow the instructions on the reverse side to vote these important matters. Vote at www.ProxyVote.com Prefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click “Sign up for E-delivery”. Voting Items Board Recommends D79355-P68606 01) Anthony Casalena 02) Andrew Braccia 03) Michael Fleisher 04) Jonathan Klein 05) Liza Landsman 06) Anton Levy 1. Election of Directors to serve until our 2023 Annual Meeting of Stockholders. Nominees: 2. Ratification of the appointment of Ernst & Young LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2022. NOTE: Such other business as may properly come before the meeting or any adjournment thereof. For For