John Kiernan

Debevoise & Plimpton LLP 

John S. Kiernan has served on the firm’s Management Committee and as Co-Chair of its Litigation Department (2002–2017), and has been Chair of its Ethics Committee since 1994. His representations have embraced a broad range of commercial disputes and internal investigations, including disputes relating to contracts, purchases and sales of businesses, corporate governance, derivative and class action claims, international treaties, securities claims, patents and other intellectual property, consumer fraud, accountant liability and mass torts.

Mr. Kiernan is recognized as a leading litigator by numerous publications. According to Chambers USA, clients praise his “great judgment,” (2010) and recognize him as “technically excellent” (2009), “incredibly creative,” “great when put in front of a board of directors” (2012) and a “superb litigator” (2011), with peers describing him as “an extremely bright, first-class litigator, thinker and colleague” (2008) and a “superstar” who applies a “deft touch rather than a sledgehammer” in commercially sensitive contract disputes, international treaty claims and securities actions (2007).

In addition, IFLR Benchmark Litigation Guide has ranked Mr. Kiernan in its top 100 commercial litigators in the United States and in New York each year since 2010 and notes “his extensive experience and breadth of knowledge.”

He is also recognized as a leading securities litigator in The Legal 500 US (2007) and as a leading litigator for commercial litigation or alternative methods of dispute resolution in numerous other “Best Lawyers” publications.

Mr. Kiernan is the Board Chair of Prisoners’ Legal Services of New York and Co-Chair of the Inner City Scholarship Fund, Lawyers Division. He has previously chaired the Boards of the International Institute for Conflict Prevention & Resolution (CPR), Legal Services-New York City, the Lawyers’ Committee for Civil Rights Under Law, Volunteers of Legal Service, the Justice Resource Center and the New York City Bankruptcy Assistance Project (which he co-founded), and was the Mayor of Pelham Manor, NY from 1999-2001.

He has also served as a director or trustee of the City Bar Justice Center, New York Alliance for the Public Schools, Practicing Attorneys for Law Students, United Way of Pelham, NY, the Pelham Art Center, the Federal Bar Council, the Village Board of Pelham Manor, the International Senior Lawyers Project and the Point O’Woods, NY Association. He served for 15 years as a volunteer coordinator for the AmeriCares/HomeFront home rehabilitation project, and for 28 seasons as a travel soccer coach.

Mr. Kiernan is the immediate past President of the New York City Bar Association, where he previously served on the Executive Committee and chaired several other committees. He has also chaired numerous committees of the Litigation Section of the American Bar Association and the Federal Bar Council.

He is the Chair of the New York Chief Judge’s Advisory Committee on Alternative Methods of Dispute Resolution, and a member of the New York State Permanent Commission on Access to Justice and the Legal Services Corporation’s Disaster Task Force, and he has previously served as Co-Chair of the New York Chief Judge’s Task Force on Hurricane Disaster Relief and a member of Chief Judge’s Committee on Non-Lawyers and the Justice Gap. He was a speaker at annual ALI-ABA Seminars on Accountants’ Liability for 12 years, and has spoken at numerous other seminars and written numerous articles on substantive issues in litigation, approaches to resolving complex disputes, and discovery.

He is the co-editor of The Litigation Manual (ABA, 3rd ed., 1999) and a contributing author of New York Business Litigation (ALM 2014) and Commercial Litigation in New York State Courts (Thomson Reuters, 4th ed., 2015), and has been an Adjunct Professor at New York University Law School.

Mr. Kiernan joined Debevoise in 1981 and became a partner in 1988. He received his B.A. in 1976 magna cum laude from Harvard and his J.D. in 1980 magna cum laude from Harvard Law School, where he was an editor of the Harvard Law Review. From 1980–1981, Mr. Kiernan served as a law clerk to the Hon. Walter R. Mansfield, U.S. Court of Appeals for the Second Circuit.


  • The board of directors of The Weinstein Company in addressing allegations of extreme sexual misconduct by its co-chairman.
  • One of the two leading fantasy sports companies in defending against Attorney General actions seeking to prohibit fantasy sports contests as illegal gambling.
  • A major shopping center company in defending against breach of contract and fiduciary duty claims for over $2 billion arising from its purchase of another shopping center partnership.
  • The Federal Reserve Bank of New York in obtaining dismissal of claims for over $40 billion against the Bank by the largest shareholder of AIG challenging the terms of a rescue loan the Bank provided to AIG during the 2008 financial crisis.
  • The Federal Reserve Bank of New York, the Federal Reserve Board of Governors, the former Secretary of the U.S. Treasury, the former Chairman of the Federal Reserve and others in a trial of class action claims against the United States arising out of the same rescue loan.
  • An NBA team in the first-ever arbitration of the fair market value of a professional sports team’s media rights.
  • Directors of a failed telecommunications company in obtaining dismissal of a $1.8 billion creditors’ claim against them, and directors of a related company in winning summary judgment rejecting $1.1 billion in fiduciary duty claims against them by bankruptcy administrators.
  • An international television company in successfully pursuing international arbitrations against the Czech Republic (based on an investor protection treaty) and a Czech business partner (based on contracts) over their mistreatment of the company, winning and recovering over $400 million for the client.
  • One of the largest manufacturers of personal computers in defending numerous consumer fraud class actions relating to claimed performance defects.
    A major publicly traded Midwestern retail chain and its directors, in defeating efforts by dissident shareholders to enjoin a proposed $1.1 billion going private transaction.
  • A cellular phone geolocation company, a maker of food preservation devices and a consortium of lenders to an airport development project in successful litigations and mediations of patent disputes.
  • A leveraged buyout sponsor in defense and settlement of a $1.2 billion action brought against it after the purchased grocery store chain failed.
  • A food services company in an internal investigation of its audit practices following its discovery of an $800 million fraud.
  • The retail leaseholder for the World Trade Center in disputes over the nature of the reconstruction at the Ground Zero site.
  • Independent trustees of a major mutual fund company in defending litigations challenging the fees paid to the funds’ advisor.


  • Harvard Law School, 1980, J.D.
  • Harvard University, 1976, B.A.

Bar Admissions:

  • New York


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What types of cases Attorney John Kiernan & Debevoise & Plimpton LLP  can handle?
Debevoise & Plimpton LLP  can handle cases related to laws concerning Corporate, Litigation, Class Action, Business, Intellectual Property. We manually verify each attorney’s practice areas before approving their profiles and reviews on our website.
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Debevoise & Plimpton LLP  is located at 919 Third Avenue, New York, NY 10022, USA. You can reach out to Debevoise & Plimpton LLP  using their phone line 212 909 6692. You can also check their website or email them at [email protected].
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