Mark Leddy


T: +1 202 974 1570
F: +1 202 974 1999

New York
T: +1 212 225 2400
F: +1 212 225 3999

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Mark Leddy is Managing Partner of Cleary Gottlieb Steen & Hamilton LLP and is based in the Washington, D.C. and New York offices.

Mr. Leddy's practice focuses on U.S. and European antitrust law, the analysis of competitive issues in mergers and acquisitions, and appearances before antitrust regulatory agencies and the courts in civil and criminal litigation. He has played a critical role in many industry-transforming transactions including Alcoa/Reynolds, Oracle/PeopleSoft, Miller/Coors, Mittal Steel/Arcelor, and Whirlpool/Maytag, and he has advised 3M, BHP Billiton, and The Coca-Cola Company, among others, in recent transactions. Mr. Leddy is recognized as a leading antitrust litigator and maintains an active docket. He is currently representing Asahi Glass, ArcelorMittal, DHL Global Forwarding, and Whirlpool in antitrust class actions, and he previously defended Otis Elevator Company and United Technologies Corporation in winning dismissal of antitrust claims in one of the first and most important court decisions applying the Supreme Court’s Twombly decision.

Mr. Leddy lectures and is widely published on criminal and civil antitrust enforcement and litigation issues.  He has also been an Adjunct Professor at Georgetown Law School.  Mr. Leddy is distinguished as a leading lawyer by Chambers Global, Chambers USA, Benchmark Litigation: The Definitive Guide to America's Leading Litigation Firms and Attorneys, Euromoney’s Legal Media Group’s Best of the Best Guide, The Best Lawyers in America and Global Competition Review’s International Who's Who of Competition Lawyers. He has been named a “Leading Lawyer” in antitrust by The Legal 500 U.S. and listed as a Best Lawyer in antitrust by Washingtonian magazine.  Mr. Leddy was also recognized in 2007 as the Chambers Antitrust Practitioner of the Year.  The BTI Consulting Group named Mr. Leddy a BTI Client Service All-Star, as nominated by corporate counsel at Fortune 1000 organizations for delivering superior client service.

Mr. Leddy joined the firm as a partner in 1986 and became Managing Partner in 2011.  From 1991 to 1994, he was resident in the Brussels office.  Mr. Leddy received a J.D. degree in 1971 and an undergraduate degree in 1969 from Boston College.  Prior to joining the firm, Mr. Leddy was with the U.S. Department of Justice for 14 years.  He joined the Antitrust Division in New York in 1972, served as Chief of the Division's Special Litigation Section in Washington, D.C. in 1978, became Deputy Director of Operations in 1981, and was named Deputy Assistant Attorney General, the highest career position in the Antitrust Division, in 1984.

Mr. Leddy is a member of the Bars in Massachusetts and the District of Columbia and is an associated member of the Bar in Brussels.  He is admitted to practice before various appellate courts and the U.S. Supreme Court.

Honors and Distinctions

Chambers Global - Competition/European Law (Expert Based Abroad): Belgium. Competition/Antitrust: United States. Competition/Antitrust (Foreign Expert).

Chambers USA - Antitrust.

Benchmark Litigation: The Definitive Guide to America's Leading Litigation Firms and Attorneys - Antitrust.

The Legal 500 U.S. - "Leading Lawyer" in Antitrust.

Euromoney's Legal Media Group’s Best of the Best Guide - Antitrust.

The Best Lawyers in America - Antitrust. International Trade and Finance. Litigation: Antitrust.

BTI Consulting Group Client Service All-Star.

Global Competition Review’s International Who's Who of Competition Lawyers

Washingtonian Best Lawyer - Antitrust.


  • Boston College Law School
    (J.D., 1971)
  • Boston College
    (B.A., 1968)

Bar Admissions

District of Columbia - 1986
Massachusetts - 1971

Areas of Law