Mark Fleming is co-chair of WilmerHale's Appellate and Supreme Court Litigation Practice. He is an accomplished and well-regarded litigator who has appeared in more than 300 appellate cases and personally presented oral argument in 72 of them, including eight oral arguments before the Supreme Court of the United States. He has also argued before the Supreme Judicial Court of Massachusetts, the Massachusetts Appeals Court, and the First, Second, Third, Eighth, Ninth, Tenth, Eleventh, Federal, and District of Columbia Circuits.
A former US Supreme Court clerk, Mr. Fleming has filed briefs in more than 50 US Supreme Court cases on topics such as patent law, immigration, criminal law and constitutional law. Mr. Fleming argues frequently in the Federal Circuit in patent cases involving various technologies and legal issues. In November 2019, he argued three complex Federal Circuit appeals for different clients in four days. In June 2022, he won vacatur of the largest patent infringement judgment in history (over $2.7 billion), which caused Litigation Daily to recognize him as “Litigator of the Week.” In April 2023, he received that honor again as part of the WilmerHale team that convinced the Federal Circuit to vacate a patent infringement judgment of over $500 million. And within a single week in June 2025, the Federal Circuit issued three favorable decisions in appeals Mr. Fleming argued, again overturning patent infringement judgments totaling over $500 million—a victory that earned him his third recognition as “Litigator of the Week.”
Mr. Fleming’s broad-based appellate experience covers numerous subject areas, ranging from patent law, securities and complex business disputes to real estate, antitrust and tax. His clients include leading companies in the fields of medical devices, life sciences, biotechnology, and pharmaceuticals, as well as high-technology industries including semiconductors, smartphones, online storage and processing, and connectivity. He also maintains an active pro bono practice, particularly in matters involving immigration law, where he has argued and won several high-profile Supreme Court cases.
In 2023, Massachusetts Governor Maura Healey appointed Mr. Fleming to be vice-chair of the Judicial Nominating Commission, which reviews all applications for judicial office in Massachusetts.
Mr. Fleming previously served as a law clerk to the Honorable David H. Souter of the Supreme Court, the Honorable Michael Boudin of the First Circuit, and the Honorable John C. Major of the Supreme Court of Canada. Mr. Fleming also served as an associate legal officer in the Appeals Chamber of the International Criminal Tribunal for the former Yugoslavia.
Updated Oct 2025
