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John F. O'Sullivan

New York

John F. O'Sullivan
+1 212 918 3000 (New York)
Practice Group

John O'Sullivan is a leading trial lawyer handling high-stakes business disputes for top global clients. Chambers and Partners describes him as a "strong presence" in the courtroom who is "brilliant at breaking down complex problems so they are easy to understand." He has more than 25 years of experience litigating a wide range of complex commercial matters.

Whether it's breach of contract and tortious interference claims or patent, trademark, and copyright litigation, John's vast experience helps him help clients. John also handles trade secret and Lanham Act actions; unfair competition, price fixing, and monopoly claims; and real estate, banking, and construction litigation. He is also actively involved in securities and corporate governance disputes and professional negligence and malpractice matters.

Numerous guides identifying top lawyers include John, such as Chambers USA, Best Lawyers in America, Super Lawyers, and Florida Trend's Legal Elite. John is also dedicated to pro bono; many legal services organizations have awarded and recognized him for his efforts on behalf of pro bono clients.

"Brilliant at breaking down complex problems so they are easy to understand. 'A strong presence.'"

Chambers & Partners

Representative experience

Prevailed in multi-jurisdiction litigation over ownership of real estate financial assets valued at nearly US$1bn.

Obtained preliminary injunction for life sciences client preserving more than US$1bn in sales.

Prevailed at trial for consumer products company in dispute over ownership of formulas for client's best-selling products.

Obtained dismissal with prejudice of securities claims seeking US$190m against a ratings agency alleging fraudulently inflated RMBS ratings.

Obtained one of the largest sanctions awards on record in Florida based on showing that principal of opposing party gave false deposition testimony.

Litigation counsel for clients in connection with many of the most prominent real estate assets in South Florida.

Established violation of the Federal Anti-Collusion Act and obtained dismissal of all claims against German financial services client.

Recovered more than US$25m for a Spanish client in disputes arising from a Florida acquisition.

Obtained a dismissal with prejudice for a major Japanese bank in a US$200m lender liability suit arising from Florida real estate investments.

Obtained a nationwide permanent injunction on behalf of a major broadcasting network in a copyright infringement suit against a satellite TV provider.

Education and admissions


  • J.D., with honors, The George Washington University Law School, 1988
  • B.A., cum laude, University of Massachusetts, 1985
  • Economics & International Relations Program, University of Sussex, 1984

Bar admissions and qualifications

  • Florida
  • New York

Court admissions

  • U.S. Bankruptcy Court, Middle District of Florida
  • U.S. Bankruptcy Court, Northern District of Florida
  • U.S. Bankruptcy Court, Southern District of Florida
  • U.S. Bankruptcy Court, District of South Dakota
  • U.S. Court of Appeals, 11th Circuit
  • U.S. Court of Appeals, 2nd Circuit
  • U.S. Court of Appeals, 7th Circuit
  • U.S. Court of Appeals, Federal Circuit
  • U.S. District Court, Middle District of Florida
  • U.S. District Court, Northern District of Florida
  • U.S. District Court, Southern District of Florida
  • U.S. District Court, Southern District of New York
  • U.S. District Court, District of Minnesota
  • U.S. Supreme Court


Commercial Litigation

Best Lawyers in America


Litigation - Banking and Finance

Best Lawyers in America


Litigation - Real Estate

Best Lawyers in America

2009-2013, 2017

Litigation: General Commercial (Florida)

Chambers USA


Business Litigation, Intellectual Property Litigation

Florida Super Lawyers


Top Rated Lawyers, Commercial Bankruptcy Creditor-Debtor Rights


Super Lawyers: Corporate Counsel, Business Litigation


Outstanding Volunteer Lawyer Award

The Legal Aid Society


Most Valuable Protector (MVP) Award

Voices for Children, Inc.


Community Advocate of the Year

11th Judicial Circuit

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