William Cavanaugh is a Senior Litigation Partner and served as Co-Chair of Patterson Belknap from 2007 to 2017. His areas of concentration include antitrust, intellectual property, and commercial litigation.
A skilled trial attorney with extensive experience in both state and federal courts as well as in arbitrations, Mr. Cavanaugh has served as national and trial counsel in many large multiparty antitrust, fraud, RICO, and consumer protection litigations in federal and state courts across the United States brought by private class action plaintiffs and State Attorneys General. His clients include major pharmaceutical, medical device, and financial services companies. Mr. Cavanaugh also served as Deputy Assistant Attorney General of the United States for Civil Enforcement in the Antitrust Division of the Department of Justice in the beginning of the Obama Administration. Mr. Cavanaugh is currently representing defendants in antitrust class actions and competitor litigations involving biologic drugs, contact lenses, educational products, and financial service products. He is also representing the lead state plaintiffs in their antitrust enforcement action against a multinational technology company. He recently led a trial team to a defense judgment in a patent infringement case involving surgical instruments and secured affirmance in the Seventh Circuit of a summary judgment ruling in a RICO case involving a pharmaceutical product.
Mr. Cavanaugh’s trial experience includes securing defense verdicts in a multibillion-dollar antitrust class action, civil fraud class actions, and representing both plaintiffs and defendants in patent trials involving medical devices and pharmaceuticals, including having successfully tried a number of Hatch-Waxman patent cases. He has also represented a number of major health care companies in arbitrated contract disputes, and has argued over two dozen appeals in appellate courts across the country.
Mr. Cavanaugh is an elected Fellow of the American College of Trial Lawyers. He has been listed in The Best Lawyers in America® for Antitrust Law and Commercial Litigation as well as in Who’s Who Legal in Litigation and the “Irish Legal 100.” Chambers USA has recognized him in the area of Intellectual Property: Patent.
Mr. Cavanaugh received his J.D. from St. John’s University School of Law and his B.S., magna cum laude, from St. John’s University.
Updated Sep 2025
- Commercial
- Competition/antitrust
- Intellectual property
- J.D. - St. John's University School of Law - 1980
- B.S., magna cum laude - St. John's University - 1977
- American College of Trial Lawyers
- American Bar Association
- American Intellectual Property Law Association
- Association of the Bar of the City of New York
- California Bar Association
- Federal Bar Council
- New York State Bar Association
- U.S. Supreme Court
- U.S. Court of Appeals, First Circuit
- U.S. Court of Appeals, Second Circuit
- U.S. Court of Appeals, Third Circuit
- U.S. Court of Appeals, Fourth Circuit
- U.S. Court of Appeals, Seventh Circuit
- U.S. Court of Appeals, Ninth Circuit
- U.S. Court of Appeals, Federal Circuit
- U.S. Court of Appeals, District of Columbia Circuit
- U.S. District Court, Southern District of New York
- U.S. District Court, Eastern District of New York
- U.S. District Court, Northern District of New York
- U.S. District Court, Western District of New York
- U.S. District Court, Central District of California
- U.S. District Court, Northern District of Illinois
- U.S. District Court, Eastern District of Wisconsin
- New York
- California