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

Filed by the Registrant ☒
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
☒	Definitive Additional Materials
☐	Soliciting Material under §240.14a-12

MARINUS PHARMACEUTICALS, 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 all boxes that apply):
☒	No fee required.
☐	Fee paid previously with preliminary materials.
☐	Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rule 14a-6(i)(1) and 0-11.

Your Vote Counts! *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 For complete information and to vote, visit www.ProxyVote.com Control # V39405-P07203 MARINUS PHARMACEUTICALS, INC. 2024 Annual Meeting Vote by May 21, 2024 at 11:59 PM EDT You invested in MARINUS PHARMACEUTICALS, 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 materials for the stockholder meeting to be held on May 22, 2024. Vote Virtually at the Meeting* May 22, 2024 9:30 a.m., Eastern Daylight Time Virtually at: www.virtualshareholdermeeting.com/MRNS2024 Get informed before you vote View the Notice and Proxy Statement and Annual Report on Form 10-K online at www.ProxyVote.com OR you can receive a free paper or email copy of the material(s) by requesting prior to May 8, 2024. 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. MARINUS PHARMACEUTICALS, INC. 5 RADNOR CORPORATE CENTER, SUITE 500 100 MATSONFORD RD RADNOR, PA 19087

Vote at www.ProxyVote.com Prefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click “Delivery Settings”. Voting Items Board Recommends V39406-P07203 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. We encourage you to access and review all of the important information contained in the proxy materials before voting. 1. Election of three Class I Directors, each to serve until the Company’s 2027 Annual Meeting of Stockholders or until such person’s successor is duly elected and qualified: For All Nominees: 01) Elan Ezickson 02) Charles Austin 03) Marvin H. Johnson, Jr. 2. Ratification of the appointment of Ernst & Young LLP as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2024. For 3. Approval, on a non-binding advisory basis, of the compensation of the Company’s named executive officers as disclosed in the proxy statement. For 4. Approval of the Marinus Pharmaceuticals, Inc. 2024 Equity Incentive Plan. For NOTE: In their discretion, the proxies are authorized to vote upon such other business as may properly come before the Annual Meeting or any adjournments or postponements thereof.