Mr. McMahon is the immediate past Chair of the firm's Business & Commercial Litigation Department, a position he held for 15 years, and was a long-standing member of the firm's Executive Committee. His litigation practice encompasses a wide range of complex corporate and commercial disputes, including securities litigation, merger and acquisition disputes, partnership disputes, intra-corporate and shareholder derivative disputes, and complex contract disputes. Mr. McMahon has litigated and tried jury and non-jury cases in the state and federal courts throughout the regional metropolitan area. He has played the leading role in numerous large class actions, enforcement proceedings with federal and state regulatory agencies, and complex adversary proceedings in the United States Bankruptcy Courts. Mr. McMahon has been the primary architect of numerous complex and multifaceted settlements involving parallel and related proceedings pending in several different courts and regulatory agencies.

Mr. McMahon has taught numerous seminars on various complex commercial and securities litigation subjects for the New Jersey Institute for Continuing Legal Education, including “Recent Developments in Class Actions and Shareholder Derivative Suits.” He is consistently recognized as a leading litigator by New Jersey Super Lawyers and Best Lawyers® publications. He was recently selected as the nominee of the United States District Judges for the District of New Jersey to the Lawyers Advisory Committee for the Third Judicial Circuit.


Mr. McMahon’s litigation practice encompasses a wide range of complex corporate and commercial disputes for companies in the food, manufacturing, chemical, financial, securities, telecommunications, and pharmaceutical industries. He has tried numerous cases in the state and federal courts in the regional metropolitan area, ranging from unfair competition to minority shareholder oppression to shareholder derivative/breach of fiduciary duty cases to a plaintiff’s financial accounting fraud case in the Eastern District of Pennsylvania (Fonda Group Ltd v. Scott Paper Company), which resulted in a substantial jury verdict and punitive damage award against the defendant.

Mr. McMahon has been actively litigating securities class actions and shareholder derivative actions in both lead and co-counsel roles for more than 30 years. His securities class action practice has included numerous cases under Sections 11 and 12 of the Securities Act of 1933, Sections 10(b) and 20 of the 1934 Act, as well as Rule 10b-5. Mr. McMahon has also represented issuers, officers and directors, broker dealers, and traders in SEC enforcement proceedings and investigations. He was the lead counsel for Sherwood Securities (National Discount Brokers), one of the largest NASDAQ wholesale market-marking firms, in connection with all aspects of the In re NASDAQ Market Markers case in the Southern District of New York and, more recently, served as co-counsel In re Synchronoss Securities Litigation, 705 F. Supp. 2d 367 (D.N.J. 2010) (GEB), class actions and Rocker Management LLC v. Lernout & Harespie, (D.N.J.) (PJS) (representing KPMG Belgium).

Mr. McMahon has also handled numerous shareholder derivative/fiduciary duty actions, including by way of example, lead counsel roles in In re Digex Shareholders Litigation (Del. Chancery), In re Educational Adventures (North Carolina Business Court), Ross v. Advance Realty Group (Del. Chancery), and co-counsel roles in In re Cendant (Superior Court of New Jersey, Chancery Division, Morris County) and In re Memory Pharmaceutical (Superior Court of New Jersey, Chancery Division, Bergen County).

Mr. McMahon is currently serving as lead litigation counsel for the plaintiff in several securities fraud actions being prosecuted in the United States District Court for the District of Delaware, relating to a massive, $2.5 billion fraud perpetrated by DBSI, Inc. and its principals, including an action against the former DBSI Insiders under Sections 10(b) and 20, James R. Zazzali, Trustee of the DBSI Estate Litigation Trust and Private Action Trust v. Douglas Swenson, et al., and a separate action under Sections 10(b) and 20, and Rule 10b-5 against approximately 70 broker dealers and their corporate parents, James R. Zazzali, Trustee for the DBSI Private Action Trust v. Advisory Group Equity Services, Ltd.


  • Seton Hall University School of Law (J.D., cum laude)
    • Phi Alpha Delta
    • Seton Hall Law Review, 1975-1977
  • Colgate University (B.A.)

Professional Activities

U.S. Court of Appeals for the Third Circuit
Lawyers Advisory Committee

Litigation Counsel of America
Senior Fellow

Lifland Inn of Court

New Jersey State Bar Association
Committee on Business & Commercial Litigation 
Committee on Class Action Lawsuits

Seton Hall University School of Law 
Lecturer, Legal Research and Writing, 1981-1982

American Judicature Society

American Bar Association

Professional Admissions

  • State of New Jersey
  • United States District Court for the District of New Jersey
  • United States Court of Appeals for the Third Circuit
  • United States Court of Appeals for the Seventh Circuit
  • United States Court of Appeals for the Ninth Circuit
  • Supreme Court of the United States

Judicial Clerkship(s)

Law secretary to the Honorable Vincent P. Biunno, United States District Judge for the District of New Jersey, 1977-1979


Listed in Chambers USA Guide to America's Leading Lawyers for Business, Litigation: General Commercial

Listed in Best Lawyers®, Commercial Litigation; Litigation - Antitrust; Litigation - Bankruptcy; Litigation - Securities
Named Newark area "Lawyer of the Year" in Litigation - Antitrust, 2013
Named Newark area "Lawyer of the Year" in Litigation - Securities, 2015

Selected to the New Jersey Super Lawyers list, Business Litigation

AV® Peer Review Rated by Martindale-Hubbell

Listed as a "Local Litigation Star" by Benchmark Litigation, 2019

Named to the Lawyers Advisory Council for the Third Judicial Circuit, 2009

No aspect of this advertisement has been approved by the Supreme Court of New Jersey. A description of the selection process methodology for the awards referenced is available at gibbonslaw.com/awards/.