TransMedics Group Inc

This Proxy Statement relates to the solicitation of proxies by the Board of Directors (“Board”) of TransMedics Group, Inc. (”TransMedics” or “Company”), for use at the 2025 Annual Meeting of Shareholders (“Annual Meeting”), and at any adjournment of that meeting. The Annual Meeting is scheduled to be held on May 22, 2025, at 8:00 A.M., Eastern Time, atwww.virtualshareholdermeeting.com/TMDX2025. On or about April 10, 2025, we will commence sending the Notice of Internet Availability of Proxy Materials (the “Notice”) to all shareholders entitled to vote at the Annual Meeting.

References throughout the Proxy Statement to “TransMedics Group, Inc.”, “TransMedics”, “we”, “us”, “our”, or the “Company” refer to TransMedics Group, Inc., unless the context otherwise indicates.

Purposes of the Meeting

The purposes of the Annual Meeting are:

Shareholders Entitled to Vote at the Meeting

Our Board has established the close of business on March 25, 2025 as the “record date” for the Annual Meeting. This means that you are entitled to vote at the Annual Meeting (and any adjournments) if our records show that you owned our common stock at that time. As of this record date, 33,824,224 shares of our common stock, including 5,445 shares of restricted stock, were issued and outstanding, held by approximately 26 registered shareholders of record. Each issued and outstanding share of common stock as of the record date is entitled to one vote on each matter properly to come before the Annual Meeting and can be voted only if the record owner of that share, determined as of the record date, is present by remote communication at the Annual Meeting or represented by proxy. A list of shareholders entitled to vote will be available for examination during the Annual Meeting atwww.virtualshareholdermeeting.com/TMDX2025.

Voting Shares That You Hold In Your Name

If you are a shareholder of record on the record date for the Annual Meeting, you may vote by proxy or you may attend the Annual Meeting and vote by remote communication at the meeting. If you do not attend the Annual Meeting, you may:

Virtual Meeting

Our Annual Meeting will be a virtual meeting, which will be conducted via live webcast. We believe hosting a virtual meeting will allow for greater shareholder attendance at the Annual Meeting by enabling shareholders who might not otherwise be able to travel to our physical meeting to attend online and participate from any location.

To participate in the Annual Meeting virtually via the Internet, please visitwww.virtualshareholdermeeting.com/TMDX2025. You will need the 16-digit control number included on your Notice, your proxy card or the instructions that accompanied your proxy materials.

Instructions should also be provided on the voting instruction card provided by your bank or brokerage firm. If you do not have your 16-digit control number and choose to attend the meeting online, you will be able to listen to the meeting only, however, and you will not be able to vote or submit questions during the meeting.

Attending the Annual Meeting

The Annual Meeting will be held entirely online atwww.virtualshareholdermeeting.com/TMDX2025. A summary of the information you need to attend the Annual Meeting online is provided below:

Webcast replay of the Annual Meeting will be available until the sooner of May 22, 2026 or the date of the 2026 Annual Meeting of Shareholders.

Technical Assistance for the Virtual Access to the Annual Meeting

We will have technicians ready to assist you with any technical difficulties you may have accessing the Annual Meeting website. If you encounter any difficulties accessing the Annual Meeting website during thecheck-in or meeting time, please call the technical support number that will be posted on the Annual Meeting login page.

Voting Shares That You Hold in Brokerage or Similar Accounts

Many shareholders hold their shares through a broker, bank or other nominee rather than directly in their own name. If you hold your shares in one of these ways, you are considered a beneficial owner, not a record owner, and you therefore have no direct vote on any matter to come before the Annual Meeting. Your broker, bank or nominee will send you voting instructions for you to use in directing the broker, bank or nominee in how to vote your shares. Your broker, bank or nominee may allow you to deliver your voting instructions via the telephone or the Internet.

A “brokernon-vote” occurs when a broker, bank or other nominee holding shares for a beneficial owner does not vote the shares on a proposal because the broker, bank or other nominee does not have discretionary voting power for a particular item and has not received instructions from the beneficial owner regarding voting. Brokers, banks or other nominees who hold shares for the accounts of their clients have discretionary authority to vote shares if specific instructions are not given with respect to routine matters. Although the determination of whether a broker, bank or other nominee will have discretionary voting power for a particular item is typically determined only after proxy materials are filed with the Securities and Exchange Commission (“SEC”), we expect that the proposal on ratification of the appointment of our independent registered public accounting firm (Proposal 3) will be a routine matter and that the election of each nominee for director (Proposal 1) and the proposal on an advisory vote on executive compensation (Proposal 2), will benon-routine matters. Accordingly, if you hold your shares through a broker, bank or other nominee and you do not timely provide your broker, bank or other nominee with specific instructions on how to vote your shares, your broker, bank or other nominee would not be authorized to cast a vote on your behalf on Proposal 1 (election of each nominee for director) or Proposal 2 (advisory vote on executive compensation), but would be authorized to cast a vote on your behalf, in its discretion, on Proposal 3 (ratification of the appointment of PricewaterhouseCoopers LLP). In such cases, a “brokernon-vote” may be

entered with respect to your shares on Proposal 1 and Proposal 2 to reflect that your broker was present with respect to your shares at the meeting but was not exercising voting rights on your behalf with respect to those shares. Brokernon-votes and abstentions will have no effect on the outcome of each proposal. Brokers, banks and other nominees generally have discretionary authority to vote on the ratification of the appointment of an independent registered public accounting firm (Proposal 3); thus, we do not expect any brokernon-votes on this matter.

Your Voting Options on Each of the Proposals

You may vote “for”, “against” or “abstain” with respect to the election of each nominee for director (Proposal 1).

You may vote “for,” “against” or “abstain” with respect to the proposal on the compensation of our named executive officers (Proposal 2).

You may vote “for,” “against” or “abstain” with respect to the proposal on the ratification of the appointment of PricewaterhouseCoopers LLP as our independent registered public accounting firm for our fiscal year ending December 31, 2025 (Proposal 3).

If any other matter is presented at the Annual Meeting, your proxy provides that your shares will be voted by the proxy holder named in the proxy card in accordance with his or her best judgment. At the time this Proxy Statement was first made available, we knew of no matters that needed to be acted on at the Annual Meeting, other than those discussed in this Proxy Statement.

Our Board’s Voting Recommendations

Our Board recommends that you vote:

If any other matter is properly brought before the Annual Meeting, the Company — through the individual named in the proxy and acting as the “proxy holder,” or his or her designee, and pursuant to the blanket authorization granted under the proxy — will vote your shares on that matter in accordance with the discretion and judgment of the proxy holder.

It is very important that your shares be represented and voted whether or not you plan to attend the Annual Meeting.

Required Votes to Approve Each Proposal

As a shareholder, you are entitled to cast one vote per share for each of the eight (8) nominees for election as directors at the Annual Meeting, but you may not cumulate your votes (in other words, you may not cast votes representing eight times the number of your shares entitled to vote in favor of a single nominee). A majority of the votes properly cast for election of a director will effect such election. However, in the event that shareholders are to select among several alternative nominees in an election of directors (such as when there are more nominees than directorships), directors will be elected from among the nominees based on those directors receiving the most “for” votes until all board seats are filled. A properly returned proxy indicating “abstain” with respect to the election of one or more directors will not be counted as a vote cast with respect to the director or directors indicated. “Brokernon-votes” will not be counted as votes cast on the proposal and will have no effect on the election of directors.

A majority of the votes properly cast at the meeting will approve: (i) the proposal to ratify the appointment of PricewaterhouseCoopers LLP as our independent registered public accounting firm for our fiscal year ending December 31, 2025; and (ii) all other matters that arise at the Annual Meeting.

Please note, however, that because the vote on the ratification of PricewaterhouseCoopers LLP is anon-binding advisory vote, the results of such vote will not be binding upon our Board or its committees.

No vote is required for approval of the compensation of our named executive officers, as this is anon-binding advisory vote. Our Board and its committees value the opinions of our shareholders and will consider the result of this vote in making future decisions relating to executive compensation arrangements.

Quorum

Massachusetts law provides that any shareholder action at a meeting requires that a quorum exist with respect to that meeting. Once a share is represented for any purpose at a meeting, it is deemed by Massachusetts law to be present for quorum purposes for the remainder of the meeting and (unless the shareholder attends solely to object to lack of notice, defective notice or the conduct of the meeting on other grounds, or a new record date is or must be set for any such adjournment) any adjournment of that meeting.

A majority of the shares of common stock entitled to vote at the Annual Meeting, present by remote communication at the meeting or by proxy, will constitute a quorum for all purposes at the meeting. If a quorum should not be present, the Annual Meeting may be adjourned from time to time until a quorum is obtained.

Shares held of record by shareholders who (by remote communication at the meeting or by proxy) abstain from voting on any or all proposals (and shares represented by “brokernon-votes,” described above under “Voting Shares That You Hold in Brokerage or Similar Accounts”) will be included in the number of shares present at the meeting for purposes of determining the presence of a quorum. However, abstentions and “brokernon-votes” as to any proposal will not be considered to be votes that have been “cast” on that proposal and therefore will not affect the outcome of the vote on any proposals described by this Proxy Statement.

Voting on Possible Other Matters

We are not aware that any person intends to propose that any matter, other than the three numbered proposals specifically described by this Proxy Statement, be presented for consideration or action by our shareholders at the Annual Meeting. If any such other matter should properly come before the meeting, however, favorable action on such matter would generally require the votes cast favoring the matter exceeding the votes opposing the matter to constitute favorable action on the matter, unless our Articles of Organization or Bylaws or applicable law require otherwise. If you vote by proxy, you will be granting the proxy holder authority to vote your shares on any such other matter in accordance with his discretion and judgment.

Revocation of Proxies or Voting Instructions

A shareholder of record who has delivered a proxy card in response to this solicitation may revoke it before it is exercised at the Annual Meeting by executing and delivering a timely and valid later-dated proxy, by a timely and valid later Internet or telephone vote, by voting by remote communication at the meeting or by giving written notice to the Corporate Secretary. Attendance at the Annual Meeting online will not have the effect of revoking a proxy unless a shareholder gives proper written notice of revocation to the Corporate Secretary before the proxy is exercised or the shareholder votes by remote communication at the meeting. Beneficial owners who have directed their broker, bank or nominee as to how to vote their shares should contact their broker, bank or nominee for instructions as to how they may revoke or change those voting directions.

Solicitation of Proxies

Our Board is making this solicitation of proxies for the Annual Meeting. We will bear all costs of such solicitation, including the cost of preparing and distributing this Proxy Statement and the enclosed form of proxy and including the cost of hosting the virtual meeting. After the initial distribution of this Proxy Statement, proxies may be solicited by mail, telephone, or personally by directors, officers, employees or agents of the Company. Brokerage houses and other custodians, nominees and fiduciaries will be requested to forward soliciting materials to beneficial owners of shares held by them for the accounts of beneficial owners, and we will pay their reasonableout-of-pocket expenses.