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William D. Marsillo


t: 914 749 8215
f: 914 749 8300
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Areas of Practice


Intellectual Property


Harvard Law School, J.D., cum laude, 1997; Lead Editor, Journal of Law and Technology

Stevens Institute of Technology, B.S.E., Valedictorian, Materials Engineering, 1994; Varsity Soccer, Captain; All-American


Hon. Lawrence E. Kahn, United States District Court for the Northern District of New York, 1998-1999

Hon. Joyce London Alexander, Magistrate Judge, United States District Court for the District of Massachusetts, 1997-1998


New York

United States Courts of Appeal: Second Circuit and Federal Circuit

United States District Courts: Southern and Eastern Districts of New York

William Marsillo's main practice area is complex business litigation.  He has represented clients in federal and state trial and appellate courts as well as domestic and international arbitrations in a variety of high-stakes matters involving intellectual property, contract disputes, fund management, corporate dissolution and other business divorces, allegations concerning breaches of fiduciary duty and corporate governance matters, class actions, partnership disputes, media rights, antitrust, and merger and acquisition disputes. Significant matters in which Mr. Marsillo has been heavily involved include the following:

  • Represented a health services technology company in a patent dispute concerning breakthrough medical diagnostic technology, which resulted in a favorable settlement during trial;
  • Lead trial lawyer on behalf of a prominent family-owned company and its officers in a corporate dissolution matter brought in New York state court by a minority shareholder;
  • Represented Brazil-based individuals and entities that engage in investment, fund, and asset management in New York federal and state courts in a dispute with a former employee in which the former employee claimed he was entitled to hundreds of millions of dollars in carried interest and other damages, which resulted in dismissal of all claims; Mr. Marsillo represented that same Brazilian group in New York federal court and ICC arbitrations in Paris concerning control rights of multi-billion dollar foreign companies;
  • Represented prominent hedge fund manager and early-stage investor on claims against a fund of hedge funds relating to rights arising from seed investment,  which resulted in successful summary judgment motion that ensured plaintiff’s rights to $70 million in interest payments and enforced plaintiff’s right to 40% membership interest in the fund of hedge funds;
  • Represented a regional sports network in an arbitration against major professional sports team, which resulted in favorable restructuring of media rights;
  • Represented a major cable provider in connection with an accounting scandal, the resulting governmental investigations and settlements, and the prosecution and defense of several complex litigations involving billion dollar claims for securities fraud and RICO, among other causes of action.

Mr. Marsillo also regularly provides business and strategic advice to his clients on a variety of matters, including governance and litigation-related matters.  He is a mediator and has successfully mediated complex business disputes pending in New York state and federal courts.  He is a member of the board of directors of Legal Services of the Hudson Valley and of the Business Council of Westchester. 

Selected Professional Awards and Associations

New York County Lawyers Association American Bar Association


How Chemical Nomenclature Confused the Courts, U. Balt. Intellectual Prop. L.J. (1999)

Morphological Transformations in Styrene-Butadiene-Styrene Triblock Copolymers, Microscopy Society of America (1995)

Related News

Family Gives Up Disputed Patent, Ending Trial With Boies' Client ((Subscription Required))

A Judge’s Wise Words on Disputes in Family-Owned Businesses (February 11, 2013)

After Opening Statement, BSF Wins Product Liability Suit for Pfizer (Winter 2010)

Pfizer v Bulger (07.28.2009)

Partner Bill Marsillo to Receive "Rising Star" Award (May 23, 2007)