John J. Sullivan


John practices in the firm's Commercial Litigation Department and has over two decades of experience handling a wide variety of complex litigation. He defends companies in securities, corporate governance, class action, antitrust, product liability, mass tort, and other business litigation. John regularly represents global companies in the life sciences, banking, consumer products, venture capital, fund management, and real estate industries.  

In the area of financial litigation, John defends clients in state and federal courts in disputes involving contested takeovers, securities class actions, RICO claims, fraud claims, and real estate financing disputes. In this area, John represents clients who have been victims of cyberattacks. He currently serves as lead counsel to a foreign central bank in the Commercial Division of the New York Supreme Court, seeking the recovery of tens of millions of U.S. dollars in foreign reserves that were stolen through a cyberattack as part of one of the largest thefts in New York banking history. John also has extensive experience in arbitration and international arbitration.

John is also a highly experienced class action litigator, having defended clients against consumer privacy, securities, antitrust, data privacy, breach of contract, and other class actions. His experience extends to multidistrict class action litigations and consolidated proceedings. He has litigated class actions involving governmental services in the pro bono sphere, and he is lead counsel to the former deputy executive director of the Port Authority of New York and New Jersey in the pending consolidated class action arising out of the “Bridgegate” scandal. 

John also has years of experience in high stakes mass tort and product liability actions, litigating bet-the-company actions in state courts and in federal multidistrict litigation.  John has served on trial defense teams in some of the largest and most challenging product liability and mass tort litigation, defending against cases involving significant personal injury and disease states and claims of failure to warn, manufacturing and design defect, and breach of warranty.

In the real estate industry, John represents lenders, REITs, and financial trusts in high-stakes litigation and advisory work regarding workouts and distressed assets, including disputes between servicers and co-lenders, and contract matters relating to distressed borrowers. John develops practical tactics for both negotiations and litigation relating to all types of distressed real estate disputes. 

A well-rounded commercial litigator, John has deep experience managing attorneys conducting case-specific discovery, defending witnesses, handling evidentiary and coordination hearings, negotiating with opponents, and deposing and defending expert witnesses. He has litigated constitutional and preemption issues, dealt with regulatory agencies and their regulations, and represented clients in appellate proceedings before state and federal appellate courts, including the U.S. Supreme Court.

Before joining Cozen O’Connor, John was a partner at Dechert LLP, and he started his career at Sullivan & Cromwell. For John's considerable success, he has been recognized by Benchmark Litigation as a “future star,” an “innovative lawyer” by the Financial Times, and as a New York Super Lawyer in Business Litigation.

John is a frequent author and speaker at legal conferences, and he is often asked to comment on current litigation in the legal media.

John earned his law degree from Rutgers University School of Law-Newark, where he was awarded the Order of the Coif and was a two-time Saul Tischler Scholar. He received his bachelor's degree from Rutgers University, New Brunswick.



Cozen O’Connor Announces Seven New Shareholders

September 07, 2023

Cozen O’Connor is pleased to announce Wendy Enerson, Melissa Grossman, Susan Grueneberg, Suzanne Radcliff, Laura Reinhart, John Sullivan, and Cheryl Upham have been promoted to shareholder.

17 Cozen O’Connor Attorneys Recognized as New York Super Lawyers and Rising Stars

September 27, 2019

Super Lawyers has named 17 Cozen O'Connor attorneys to its 2019 New York Super Lawyers and Rising Stars list.

FDA Alert on Hacking Vulnerability in Heart Defibrillators is Wake-Up Call: Lawyers

March 28, 2019

John Sullivan was quoted in Law360's recent article on the U.S. Food and Drug Administration's recent safety alert last week about the vulnerability to hacking of up to 750,000 implantable heart defibrillators.

18 Cozen O'Connor Attorneys Named New York Metro Super Lawyers and Rising Stars

September 21, 2018

Super Lawyers has named 17 Cozen O'Connor attorneys to its 2018 New York Super Lawyers and Rising Stars list. Twelve were recognized as Super Lawyers and five were named "Rising Stars."

Texas Suit Over Death Penalty Drug Faces Steep Odds

May 10, 2017

John Sullivan, a member of Cozen O'Connor's Commercial Litigation department, discusses Texas's uphill battle against the U.S. Food and Drug Administration in its suit over the agency’s import ban of a drug used to carry out lethal injection executions.


The Canary in the Coal Mine Isn’t Looking So Good Anymore

December 04, 2018

John Sullivan, a member of the firm's Commercial Litigation Department, authored the blog, "The Canary in the Coal Mine Isn’t Looking So Good Anymore" for the Drug & Device Law blog.

MDL Court in the Testosterone Replacement Therapy Litigation Throws Out Another Large Jury Verdict

July 13, 2018

John Sullivan, a member in the firm's Commercial Litigation Practice, authored, "MDL Court in the Testosterone Replacement Therapy Litigation Throws Out Another Large Jury Verdict," for the Drug & Device Law Blog.

Personal Jurisdiction through Alter Ego Fails in Illinois

June 29, 2018

John Sullivan, a member in the firm's Commercial Litigation Practice, authored, "Personal Jurisdiction through Alter Ego Fails in Illinois" for the Drug and Device Law Blog.

New York Court of Appeals Rejects Litigation Science under Frye Standard [Products Liability Prevention & Defense Blog]

March 08, 2016

Put quotes around the phrase “litigation science” and Google it.  Go ahead, we’ll wait. . . . . What did you find?  Not good, right.  You found a lot.  Too much.  The first Google page alone shows how controversial this subject is.  For instance, you’ll find references to Ninth Circuit Judge Alexi...

Should We Expand the Collateral Source Rule? No Thanks [Drug and Device Law]

October 26, 2015

John Sullivan discusses the Louisiana Supreme Court case Hoffman v. 21st Century North Am. Ins. Co., in which the plaintiff attempted to expand the collateral source rule to allow recovery of medical costs that were never actually billed.

Events & Seminars

Past Events

Litigating through the Coronavirus

April 17, 2020 - Webinar


  • Rutgers University School of Law—Newark, J.D., 1996
  • Rutgers University, New Brunswick, B.A., 1992

Awards & Honors

New York Super Lawyer in Business Litigation 2018, 2019. This award is conferred by Super Lawyers. A description of the selection methodology can be found here. No aspect of this advertisement has been approved by the Supreme Court of New Jersey.

  • New York
  • New Jersey
  • U.S. Supreme Court
  • U.S. Court of Appeals for the Second Circuit
  • U.S. District Court -- New Jersey
  • U.S. District Court -- Southern District of New York
  • U.S. District Court -- Eastern District of New York