Yvonne Hennessey

Yvonne chairs Barclay Damon’s Environmental and Lobbying & Election Law Compliance Practice Areas and co-leads its Oil & Gas, Linear Infrastructure, and Energy Markets Teams. Her environmental practice centers on project siting and environmental and regulatory litigation in administrative and judicial forums. She advises clients on addressing opposition to proposed projects and developing a position for litigation that may follow. Her work spans manufacturing and development, with a particular focus on the energy and semiconductor industries.

In project permitting and siting, Yvonne advises on federal, state, and local requirements, including those arising under the Clean Air Act, Clean Water Act, Coastal Zone Management Act, and related state laws. Her work also covers environmental review under the National Environmental Policy Act and New York State Environmental Quality Review Act. She represents clients in proceedings before state regulatory commissions involving electric and gas infrastructure and supply, including matters concerning appropriate cybersecurity protections.

Yvonne handles complex commercial, regulatory, and permitting disputes. Her litigation experience includes permit challenges, cost-recovery actions under the Comprehensive Environmental Response, Compensation, and Liability Act, Navigation Law claims, and actions under the Resource Conservation and Recovery Act. She also assists clients facing enforcement matters brought by state and federal regulatory authorities.

Beyond her environmental work, Yvonne counsels clients on state and federal lobbying and election laws. She advises on lobbying registration and reporting obligations, campaign contributions and reporting, and questions involving compliance and potential civil or criminal exposure. Chambers & Partners has described her as “an absolutely amazing professional” and noted that her “experience and professionalism is paramount.”

• Successfully defended before the Second Circuit Court of Appeals a challenge to the water quality certificate issued by the New York State Department of Environmental Conservation for an interstate natural gas pipeline.
• Serves as co-lead counsel to the SEQRA lead agency in support of the environmental review of Micron’s proposed $100 billion semiconductor chip manufacturing facility proposed for Clay, New York, including regular interfacing with federal and state regulatory agencies.
• Served as co-lead counsel to the Onondaga County Industrial Development Agency (OCIDA) on the expansion of the White Pine Commerce Park in Clay, New York, in support of the planned $100 billion Micron semiconductor chip manufacturing facility. Coordinated the Final Supplemental Generic Impact Statement for the expansion of the commerce park.
• Successfully defended an electric generating facility in multiple challenges to its Clean Air Act and Clean Water Act operating permits, including successful decisions on appeal.
• Challenged the NYSDEC’s authority under the Climate Leadership and Community Protection Act, resulting in a ruling that the agency’s application of the law was both an error of law and arbitrary and capricious.
• Successfully defended a client in a class action lawsuit seeking over $260 million in property and personal injury damages as well as medical monitoring regarding the disposal of waste at a landfill. Ultimately secured dismissal with prejudice prior to fact depositions or expert discovery.
• Represents the Dormitory Authority of the State of New York as environmental counsel for the construction of the New York State Life Sciences Public Health Laboratory to centralize and consolidate existing operations of the Wadsworth Center that are currently located in five separate facilities throughout the Capital Region.

• Northeastern University School of Law, JD
• State University of New York at Geneseo, BA

Admitted to Practice

• New York
• Pennsylvania
• Massachusetts

Court Admissions

• US Court of Appeals for the Second Circuit
• US District Court for the District of Massachusetts
• US District Court for the Eastern District of New York
• US District Court for the Northern District of New York
• US District Court for the Southern District of New York
• US District Court for the Western District of New York

• The Best Lawyers in America®: Litigation – Environmental, 2013–2027
• Chambers USA, Upstate New York: Environment, 2020–2026
• Selected to Super Lawyers Upstate New York: Energy, 2013–2021; Environmental Litigation, 2013–2026
• Selected to Super Lawyers Upstate New York: Top 50, 2026; Top 25 Women, 2026
• The Best Lawyers in America®: Albany "Lawyer of the Year": Litigation – Environmental, 2025
• Super Lawyers: Top 25: Hudson Valley Super Lawyers, 2024
• City & State New York, Trailblazers in Law List, 2024
• New York State Bar Association Environmental Law Section, Brightest Young Member, 2010

• Barclay Damon’s Women’s Forum
• Independent Oil & Gas Association of New York
• Institute for Energy Law, Advisory Board Member
• Institute for Energy Law, Oil & Gas E-Report, Editor

Bar Associations

• New York State Bar Association, Environmental and Energy Law Section, Past Chair
• Capital District Women’s Bar Association
• Northern District of New York Federal Court Bar Association, Past-President
• Women's Bar Association of the State of New York