Ecovyst Inc.

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 ☒ 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 Pursuant to §240.14a-12

Ecovyst 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):

☒ No fee required.

☐ Fee paid previously with preliminary materials.

☐ Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11

600 Lee Road, Suite 200Wayne, Pennsylvania 19087

April 8, 2025

Dear Stockholder:

We cordially invite you to attend our 2025 Annual Meeting of Stockholders on Thursday, May 8, 2025 at 8:30 a.m. (Eastern Time), to be conducted exclusively via live webcast atwww.virtualshareholdermeeting.com/ECVT2025.

The proxy statement accompanying this letter describes the business we will consider at the annual meeting. Your vote is important regardless of the number of shares you own. Whether or not you plan to attend the annual meeting, we encourage you to consider the matters presented in the proxy statement and vote as soon as possible. Instructions for Internet and telephone voting are attached to your proxy card. If you prefer, you can vote by mail by completing and signing your proxy card and returning it in the enclosed envelope.

We hope that you will be able to join us on May 8 th.

Sincerely,

Kurt J. Bitting

Director and Chief Executive Officer

2025 PROXY STATEMENT

600 Lee Road, Suite 200Wayne, Pennsylvania 19087

NOTICE OF ANNUAL MEETING OF STOCKHOLDERS

The 2025 Annual Meeting of Stockholders (the “Annual Meeting”) of Ecovyst Inc. (the “Company”) will be a virtual meeting conducted exclusively via live webcast atwww.virtualshareholdermeeting.com/ECVT2025 on Thursday, May 8, 2025 at 8:30 a.m. (Eastern Time) for the following purposes as further described in the Proxy Statement accompanying this notice:

Stockholders of record at the close of business on March 24, 2025 are entitled to notice of, and entitled to vote at, the Annual Meeting and any adjournments or postponements thereof.

The Company has determined to hold a virtual annual meeting in 2025 in order to facilitate stockholder attendance and participation by enabling stockholders to participate from any location and at no cost. You will be able to attend the Annual Meeting online, vote your shares electronically and submit questions during the meeting by visitingwww.virtualshareholdermeeting.com/ECVT2025. To participate in the virtual meeting, you will need the control number included on your proxy card or voting instruction form. The meeting webcast will begin promptly at 8:30 a.m. (Eastern Time). We encourage you to access the meeting prior to the start time. Online check-in will begin at 8:15 a.m. (Eastern Time), and you should allow ample time for the check-in procedures. If you encounter any difficulties accessing the virtual meeting during the check-in or meeting time, please call the technical support number that will be posted on the virtual stockholder meeting log in page.

By Order of the Board of Directors,

Joseph S. Koscinski

Secretary

Wayne, Pennsylvania

April 8, 2025

2025 PROXY STATEMENT

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