MERCURY SYSTEMS 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

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Notice of 2026 Annual Meeting of Shareholders

Dear Shareholders:

The Board of Directors of Mercury Systems, Inc. invites you to attend the 2026 Annual Meeting of Shareholders. The Annual Meeting will be held on October 28, 2026, at 10:00 a.m. Eastern Time at the Company's headquarters at 50 Minuteman Road, Andover, Massachusetts 01810. The meeting is being held for the following purposes:

•To elect three Class II directors nominated by the Board of Directors, each to serve for a three-year term, and in each case until their successors are duly elected and qualified.

•To hold an advisory vote on the fiscal 2026 compensation of our named executive officers (the "say-on-pay" vote).

•To ratify the appointment of KPMG LLP as our independent registered public accounting firm for fiscal 2027.

•To consider and act upon any other business that may properly come before the meeting or any adjournment or postponement of the meeting.

The first proposal relates solely to the election of three Class II directors and does not include any other matters relating to the election of directors, including, without limitation, the election of directors nominated by any Mercury shareholder.

The Board of Directors has fixed the close of business on September 1, 2026 as the record date for the meeting. All shareholders of record on that date are entitled to notice of and to vote at the meeting.

Your vote is important. Please vote by internet, telephone, or mail as soon as possible to ensure your vote is recorded promptly. Please also note that, if you wish to attend the meeting, you must request an admission ticket in advance by contacting us at annualmeeting@mrcy.com. To attend the meeting, please note the security procedures included on page 1 of the proxy statement.

Important Notice Regarding the Availability of Proxy Materials for the 2026 Annual Meeting of Shareholders to be held on October 28, 2026: The proxy statement and annual report to shareholders for our fiscal year ended July 3, 2026 are available at www.envisionreports.com/MRCY.

By Order of the Board of Directors

Chairman of the Board, President, and Chief Executive Officer

Andover, Massachusetts

September 17, 2026

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EXECUTIVE SUMMARY

This executive summary is an overview of information that you will find elsewhere in this proxy statement. This summary does not contain all of the information that you should consider, and you should read the entire proxy statement carefully before voting.

Proposals and Board Recommendations

Cautionary Note on Forward-Looking Statements: This proxy statement contains certain forward-looking statements, as that term is defined in the Private Securities Litigation Reform Act of 1995, including those relating to our focus on enhanced execution of our strategic plan. You can identify these statements by the words "may," "will," "could," "should," "would," "plans," "expects," "anticipates," "continue," "estimate," "project," "intend," "likely," "forecast," "probable," "potential," and similar expressions. These forward-looking statements involve risks and uncertainties that could cause actual results to differ materially from those projected or anticipated. Such risks and uncertainties include, but are not limited to, cost increases, our inability to increase production and deliver products on time and with appropriate quality, continued funding of defense programs, the timing and amounts of such funding, general economic and business conditions, including unforeseen weakness in the Company's markets, effects of any U.S. federal government shutdown or extended continuing resolution, effects of increasingly volatile geopolitical events and regional conflicts, competition, changes in technology and methods of marketing, delays in or cost increases related to completing development, engineering and manufacturing programs, changes in customer order patterns, changes in product mix, continued success in technological advances and delivering technological innovations, changes in, or in the U.S. government's interpretation of, federal export control or procurement rules and regulations, including tariffs, changes in, or in the interpretation or enforcement of, environmental rules and regulations, market acceptance of the Company's products, shortages in or delays in receiving components, supply chain delays or volatility for critical components, production delays or unanticipated expenses including due to quality issues or manufacturing execution issues, failure to meet contractual performance specifications, adherence to required manufacturing standards, capacity underutilization, increases in scrap or inventory write-offs, failure to achieve or maintain manufacturing quality certifications, such as AS9100, failure to achieve or maintain qualified business systems, such as those required by the DFARS, adverse findings in government audits or investigations, the impact of supply chain disruption, inflation and labor shortages, among other things, on program execution and the resulting effect on customer satisfaction, inability to fully realize the expected benefits from acquisitions, restructurings, and operational efficiency initiatives or delays in realizing such benefits, challenges in integrating acquired businesses and achieving anticipated synergies, effects of shareholder activism, increases in interest rates, changes to industrial security and cyber-security regulations and requirements and impacts from any cyber or insider threat events, including the risks from heightened, persistent, and increasingly sophisticated nation-state level cyberattacks and emerging threats associated with agentic AI-enabled cyber tools, changes in tax rates or tax regulations, changes to interest rate swaps or other cash flow hedging arrangements, changes to generally accepted accounting principles, difficulties in retaining key employees and customers, litigation, including the state law claim related to our settled federal securities class action lawsuit, unanticipated costs under fixed-price service and system integration engagements, and various other factors beyond our control. These risks and uncertainties also include such additional risk factors as are discussed in the Company's filings with the U.S. Securities and Exchange Commission, including its Annual Report on Form 10-K for the fiscal year ended July 3, 2026 and subsequent Quarterly Reports on Form 10-Q and Current Reports on Form 8-K. The Company cautions readers not to place undue reliance upon any such forward-looking statements, which speak only as of the date made. The Company undertakes no obligation to update any forward-looking statement to reflect events or circumstances after the date on which such statement is made.

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Company Overview

Mercury Systems is a global leader in aerospace and defense electronics, providing breakthrough capabilities in signal and data processing. With a four-decade legacy of innovation that spans silicon to systems and radio frequency front ends to effectors, we accelerate commercial technology adoption to deliver powerful and secure mission-critical processing solutions to the edge. Our end-to-end processing ecosystem, the Mercury Processing Platform, is built on technologies we have developed and acquired over 40 years. Our technologies are available as standard products or custom solutions from silicon to system scale to ensure interoperability, reduced complexity, optimized performance and speed of development.

Named Executive Officers

Our named executive officers for our 2026 fiscal year are:

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Our Board of Directors

The following table provides summary information about our Directors as of the date of this proxy statement.

We are proposing that Jean Bua, Gerard J. DeMuro, and Scott Ostfeld, three continuing Class II directors, be elected to serve terms of three years, and in each case until their successors are duly elected and qualified or until they sooner die, resign, or are removed. With respect to the nominees for Class II director standing for election at the meeting, Ms. Bua was appointed to the Board in 2025, Mr. DeMuro was appointed to the Board in 2023, and Mr. Ostfeld was appointed to the Board in 2023.

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Environmental, Social, and Corporate Governance Highlights

Governance

Our focus on good corporate governance stems from our belief that a strong governance framework creates long-term value for our shareholders, strengthens Board and management accountability, and builds trust in us and our brand. Our governance framework for our 2026 fiscal year included the following highlights:

Our Board of Directors and executives understand and embrace the importance to all of our primary stakeholders of environmental, social, and governance ("ESG") measurement and reporting. For a number of years, we have been focused on the aspects of ESG we believe have the greatest impact on our business, our stakeholders, and value creation. As it relates to the environment and sustainability, our initial priorities include: talent management and culture; responsible sourcing and operational excellence; cyber security; and environmental stewardship. We have also focused on addressing a number of key governance principles that are generally considered best practices. Of our areas of focus, we are more focused on developing talent management and culture and cyber security because we believe these have the greatest potential to create - and the highest risk to destroy - value for Mercury and our shareholders. We continue to invest in our efforts, results, and reporting accountability, and endeavor to add both to what we do and how we report these efforts over time.

Our executive leadership team oversees and implements our environmental initiatives with a view toward demonstrating our commitment to good corporate citizenship and responsible business practices. The Human Capital and Compensation Committee of our Board of Directors reviews our ESG practices with a view toward how our efforts help attract, develop, and retain employee talent, including our culture and values as well as how we demonstrate our commitment to good corporate citizenship. The Nominating and Governance Committee of our Board of Directors is responsible for the annual assessments of the Board, its Committees, and individual directors, the annual process of the selection and nomination of directors for election, our corporate governance policies and processes, and reviewing and overseeing Mercury's environmental impact and initiatives.

Talent Management

For talent management and culture, we strive to invest in the professional development of our team members. We are focused on ongoing employee training in critical compliance areas and on business ethics, export rules, and our culture of integrity. Adhering to high ethical and security standards and operating with integrity are foundations of our culture and values. We disclose in the Environmental, Social, and Governance section of our website our voluntary and involuntary termination rates and our OSHA injury rates.

Cyber and Industrial Security

The layers of cyber security we have built into our business systems and incorporated into our processes help ensure the critical data that drives the development of customer solutions is secure and protects our employees' personal information. We remain focused on modeling industry best practices and following evolving regulations. Through integrated collaboration

vi and a commitment to secure innovation, we achieved Cybersecurity Maturity Model Certification (CMMC) 2.0 compliance as soon as the rule took effect.

We have cyber security expertise on our Board of Directors, with Ms. Plunkett having served as a federal senior executive at the National Security Agency (NSA), including roles as Deputy Director and later Director of Information Assurance, where she led the agency's information assurance and cyber defense mission.

We have deployed and have been relying upon an industrial security program with superior ratings from the U.S. Defense Counterintelligence and Security Agency (DCSA). Six of our cleared sites have been recognized with the James S. Cogswell Industrial Security Achievement Award in recent years; less than 1% of the 13,000+ cleared contractor locations receive this award annually.

Responsible Sourcing

We believe responsible sourcing and operational excellence are integral parts of value creation. We work with all our suppliers in an effort to ensure that we all adhere to an equal and high standard of sustainability and ethical principles. We provide opportunities for small businesses to engage with us as we support our customers in the aerospace, defense, and intelligence markets. We work closely with many categories of small businesses, including small disadvantaged, women-owned, veteran-owned, service-disabled veteran-owned, and historically underutilized business zone (HUBZone) companies.

Our performance excellence initiatives include a focus on supply chain efficiency and procurement savings, which we believe will further enhance our competitiveness and value in the coming years.

Environmental Stewardship

As a technology company, we have relatively limited exposure to environmental stewardship risks in our operations. Nonetheless, we are focused on promoting environmental stewardship and introducing innovative processes and technologies that improve our efforts, including quantifying and disclosing our environmental impact along with our efforts to maximize future generations' ability to live, work, and play in our shared natural environment. We disclose in the ESG section of our website details of scope 1, scope 2, and scope 3 greenhouse gas (GHG) emissions from our business activities covering backup-generators and boilers for scope 1 emissions, purchased energy for scope 2 emissions, and business travel for scope 3 emissions. We have partnered with a nationally recognized waste management vendor to ensure that our by-products and materials are reclaimed, recycled, or disposed of in ways that will reduce environmental impacts and conserve natural resources. As an environmentally conscious company, we focus on and support efforts that move towards a zero-waste future through continuous improvement of production processes, sustainable materials management, and resource efficiency.

Facilities optimization and capital and asset efficiency are significant themes in our operational excellence initiatives, and we believe we will create further value for all of our stakeholders as we use our resources more efficiently.

Further Information

Please see the Environmental, Social, and Governance section of our website, www.mrcy.com, under "Company" for detailed disclosures on our commitment to sustainability and ESG practices. Information contained on our website and social media channels does not constitute part of this proxy statement or our Annual Report on Form 10-K.

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TABLE OF CONTENTS

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