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

MP MATERIALS CORP.

(Name of Registrant as Specified In Its Charter)

N/A

(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 Rules 14a-6(i)(1) and 0-11.

MP MATERIALS MP MATERIALS CORP. 6720 VIA AUSTI PARKWAY, SUITE 450 LAS VEGAS, NV 89119 D73845-P66070 Your Vote Counts! MP MATERIALS CORP. 2022 Annual Meeting on June 14, 2022 Vote by June 13, 2022 11:59 PM Eastern Time You invested in MP MATERIALS CORP. 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 June 14, 2022. Get informed before you vote View the Notice of Annual Meeting, Proxy Statement and 2021 Annual Report online OR you can receive a free paper or email copy of the material(s) by requesting prior to May 31, 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. We encourage you to access and review all of the important information contained in the proxy materials before voting. PV For complete information and to vote, visit www.ProxyVote.com Control # Smartphone users Point your camera here and vote without entering a control number Vote Virtually During the Meeting* June 14, 2022 10:30 AM Pacific Time Virtually at: www.virtualshareholdermeeting.com/MP2022 *Please check the meeting materials for any special requirements for meeting attendance. V1.1

Vote at www.ProxyVote.com 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. Voting Items Board Recommends 1. Election of 3 Directors Named in the Proxy Statement Nominees: 1a. Connie K. Duckworth For 1b. Maryanne R. Lavan For 1c. General (Retired) Richard B. Myers For 2. The ratification of the appointment of KPMG LLP as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2022. For 3. Advisory vote to approve compensation paid to the Company’s named executive officers. For 4. Advisory vote on the frequency of future advisory votes on compensation of the Company’s named executive officers. 1 Year NOTE: The proxies are authorized to vote in their discretion upon such other business as may properly come before the meeting or any adjournment or postponement thereof. Prefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click “Sign up for E-delivery”. D73846-P66070