William Cavanaugh is a senior litigation Partner and served as Co-Chair of the Firm 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 several large multiparty antitrust, fraud and consumer protection litigations in federal and state courts across the United States brought by private plaintiffs and state attorneys general. His clients include major pharmaceutical, medical device, food and beverage, and financial services companies. Mr. Cavanaugh also served as Deputy Assistant Attorney General for Civil Enforcement in the Antitrust Division of the United States 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 also includes securing defense verdicts in a multi-billion dollar antitrust class action, civil fraud class actions and representing a plaintiff medical device manufacturer in back-to-back jury verdicts of $325 million and $271 million in patent infringement cases against two competitors. He has successfully tried a number of Hatch-Waxman patent cases and represented a number of major health care companies in arbitrated contract disputes.

Mr. Cavanaugh is an elected Fellow of the American College of Trial Lawyers. He was recognized as a “National Practice Area Star” and a “Litigation Star” for New York in the areas of Antitrust, General Commercial, and Intellectual Property by Euromoney Institutional Investor PLC's  Benchmark Litigation, and was named the Best Lawyers® 2015 Litigation - Antitrust “Lawyer of the Year” in New York City. He is also recognized in Chambers USA.

With respect to his antitrust work, clients quoted in Benchmark have called Mr. Cavanaugh “one of the best antitrust lawyers to be found anywhere.” One stated that, “Bill has an amazing depth of experience and knowledge in antitrust. From a counselling perspective, he is able to give quick guidance and recommendations, which many attorneys are hesitant to do.Chambers USA noted that his, “antitrust practice covers a broad spectrum of industries, including pharmaceuticals and financial services. Sources are quick to highlight his ‘big trial record’ and agency experience as particular strengths.” In 2021, Patterson Belknap was named to a list of law firms representing the top ten companies with the highest market capitalization facing antitrust litigation in the technology, pharmaceutical, and financial sectors, according to a Bloomberg Law analysis

Chambers USA, also recognized Mr. Cavanaugh for his patent litigation skills. Sources “describe him as ‘very accomplished’ and ‘a strong first chair’” in his representation of “marquee clients in business-critical patent cases.” The guide states that, “[t]he ‘formidable’ William Cavanaugh, observers comment, is ‘an excellent trial lawyer and strategist, quick on his feet and excellent at conveying points clearly and persuasively in the courtroom.’ He represents a fine choice of counsel for cases in the technology and life sciences sectors.”

  • U.S. Supreme Court
  • U.S. Court of Appeals, First Circuit; Second Circuit; Third Circuit; Fourth Circuit; Seventh Circuit; Ninth Circuit; Federal Circuit; District of Columbia Circuit
  • U.S. District Court, Southern, Eastern, Western and Northern Districts of New York; Central District of California; Northern District of Illinois; Eastern District of Wisconsin
  • New York
  • California
Professional Activities

MEMBERSHIPS: Fellow, American College of Trial Lawyers; Member, 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

HONORS: Recognized in Who’s Who Legal: Litigation 2017 - 2021; Recognized in Chambers USA in the area of Intellectual Property: Patent; Named the Best Lawyers® 2015 Litigation - Antitrust “Lawyer of the Year” in New York City; Listed as a "Litigation Star" for New York in Euromoney Institutional Investor PLC’s Benchmark: America's Leading Litigation Firms and Attorneys; Named in Super Lawyers in the area of Antitrust and Commercial Litigation; Named to the "Irish Legal 100"