William Walsh is a senior counsel within the Environmental Unit with over 30 years of litigation experience. Prior to joining Berger Montague, he was part of the environmental team at a major plaintiff firm in Manhattan for 16 years. Mr. Walsh has played a significant role representing several states and municipal water providers in actions against polluters for groundwater contamination, particularly PCE and MTBE. He has developed a detailed understanding of water production practices and the hydrogeological issues associated with contaminant migration within aquifers. He has also represented a community directedly impacted from PFOA contamination in its aquifer and represented individuals in toxic tort cases involving PFOA and Roundup.

Mr. Walsh graduated from Haverford College with a degree in political science and worked as a legislative assistant on a Senate staff for two years before attending law school. At the University of Minnesota Law School, he was a member of the Minnesota Law Review and a moot court director.

Mr. Walsh has been an active member of his local community, serving as a trustee for six years on the Hendrick Hudson Central School District Board of Education, as well as coaching various soccer teams. He has served as an officer or on the Board of Directors of the Lincoln Society of Peekskill, the oldest continuous society dedicated to President Lincoln, for 20 years. Mr. Walsh is an invested member of the Baker Street Irregulars.

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  • In re Bundles, Finding a New Basis for Determining “Reasonably Equivalent Value” Under Section 548 of the Bankruptcy Code, 40 DePaul L. Rev. 175 (1990).
  • Halpern, Court of Appeals Sharply Diminishes the Substantive Due Process Rights of Property Owners in New York, 11 NYSBA NY Litigator 16 (Spring 2006)(authored).
  • Canon Law: Lawyers, Law and the Sherlockian Canon (W. Walsh & D. Zaldin eds., Baker Street Irregular Press 2018).
  • William A. Walsh, Marfan Syndrome: Seeking History in a Tall Tale in Stimulating Medicine (Robert Katz and Andrew Solberg, eds., Baker Street Irregular Press 2022)
  • William A. Walsh, Asteroids, Comets and the Structure of the Solar System in My Scientific Methods Dana Richards, ed., Baker Street Irregular Press 2022)
  • William R. Walsh & William A. Walsh, Lusitania: Elegance and Tragedy, in The Green Bag’s Almanac & Reader 2021 (Green Bag Press 2021)
  • William A. Walsh, Stained Reputations – High Treason in “The Second Stain,” in Irregular Stain (Robert Katz and Andrew Solberg, eds., Baker Street Irregular Press 2014)


  • Member – New York Bar
  • Member – New Jersey Bar
  • Member – West Virginia Bar (inactive)
  • Admitted – Eastern, Southern, Northern & Western Districts of New York
  • Admitted – District Court of New Jersey
  • Admitted – Second Circuit Court of Appeals
  • Admitted – United States Supreme Court