Brian K. Mahanna


  • Co-Chair, State Attorneys General Practice

Brian K. Mahanna provides strategic counsel to clients facing high-profile and complex investigations, corporate crises, regulatory scrutiny and other significant challenges, particularly when law and public policy converge. With years of state and local government experience—including at the head of one of the nation’s largest and most active state attorney general’s offices, and as senior advisor to the mayor of New York—Mr. Mahanna is uniquely positioned to advise and assist clients with complex regulatory issues at all levels of government.

As chief of staff and deputy attorney general in the Office of the New York State Attorney General, Mr. Mahanna was responsible for the office’s operations and served as the primary liaison to the governor’s office, the state legislature, state agencies and other state attorneys general, including on complex multi-state investigations and litigation. He also supervised all major civil, regulatory and criminal cases, investigations, legal positions and initiatives for a state at the center of the nation’s financial sector and other important industries and managed the Executive Division’s special counsels and the communications, data analytics, legislative and intergovernmental affairs departments.

Mr. Mahanna advises companies facing public controversies in multiple arenas, such as when state attorneys general and other state regulators launch investigations along with Congress and federal agencies. In both the public and private sectors, Mr. Mahanna has litigated across multiple jurisdictions and overseen highly publicized corporate investigations and white collar cases. His extensive policy and litigation experience give him a deep understanding of how government agencies approach issues within their purview and critical insight into the regulatory frameworks that govern his clients’ industries. He possesses the specific skillset needed to address the wide-ranging and complicated legal and reputational challenges presented by the increasingly commonplace investigations, litigation and enforcement actions launched by state attorneys general or other state and local regulators in areas as diverse as consumer privacy and data security, sports gaming, broadband, alternative lending and crypto products, and non-traditional modes of transportation.

Before joining the Office of the New York Attorney General, Mr. Mahanna was in private practice, working on complex civil and criminal matters, with a focus on municipal and state government-related proceedings. He also served as senior adviser to former New York City Mayor Michael Bloomberg and as chief of staff and counsel to the deputy mayor for operations. In this role, Brian managed the operations of many of the city’s law enforcement and regulatory agencies. 

Mr. Mahanna was named to Bloomberg Law’s inaugural “They’ve Got Next: 40 Under 40” list for White Collar, Investigations & Crisis Leadership.

Professional Activities

Mr. Mahanna is a trustee of the Citizens Budget Commission of New York and Citizens Union of New York, as well as a member of the New York City Bar Association’s Committee on New York City Affairs. 


  • State AG Investigations and Engagement

    • Serve as strategic and settlement counsel for Walmart concerning thousands of opioids cases brought or contemplated by myriad plaintiffs, including the State Attorneys General, tribal nations, and local governments and private and institutional plaintiffs. Successfully negotiated nationwide resolution with all 50 States and territories, all tribal nations, and thousands of local governments and affiliated entities.
    • Lead counsel in responding to an investigation by all 50 State Attorneys General relating to the effects of the company’s technology on users.
    • Counsel a national pharmacy chain concerning inquiries by multiple state attorneys general regarding COVID-19 vaccine privacy issues. 
    • Represented an online software company in multi-fora consumer protection investigations and litigation, including by the Federal Trade Commission, state attorneys general, a state regulator and state subdivisions. Negotiated successful settlement of claims of all state attorneys general.   
  • State Regulatory Investigations

    • Represented a financial services company in a cybersecurity investigation and enforcement action conducted by the New York Department of Financial Services.
    • Represent a technology company in an investigation by a state banking and insurance regulator regarding its advertising policies.
    • Represented a major national distributor of personal protective equipment in a price gouging investigation. 
  • Public Policy and Legislative Affairs

    • Advised tribes and sports gambling companies concerning federal and state gaming and tribal gaming issues in connection with sports gambling legalization campaign in multiple states.
    • Advised a technology company concerning New York regulatory issues and proposed legislation related to independent contractors and worker misclassification. 
  • Comprehensive Strategic Counsel

    • Counsel a sports gaming operator concerning strategy and compliance regarding state laws relating to gaming and interactive fantasy sports, and represent the company in investigation by state gaming regulator.
    • Conducted internal investigation for national retail chain concerning employment law compliance issues and advised on strategy for remediation and regulatory engagement. 
    • Devise a nationwide public policy, advocacy and litigation strategy for Period Equity, a nonprofit advocacy organization dedicated to eliminating the state sales tax on menstrual products, known as the “Tampon Tax.”
    • Counseled over a dozen companies, across a broad range of industries, regarding state and local executive orders and other regulatory and legislative responses to the coronavirus (COVID-19) pandemic.

Insights & News


  • Education

    • JD, Yale Law School, 2009

    • BA, Political Science and Metropolitan Studies, New York University, 2003

      magna cum laude
  • Admissions

    • New York

    • US District Court for the Eastern District of New York

    • US District Court for the Southern District of New York

  • Government Experience

    • State and Local Government

      Chief of Staff and Deputy Attorney General, New York
    • State and Local Government

      Senior Advisor to the Mayor, Office of the Mayor of New York City



Unless you are an existing client, before communicating with WilmerHale by e-mail (or otherwise), please read the Disclaimer referenced by this link.(The Disclaimer is also accessible from the opening of this website). As noted therein, until you have received from us a written statement that we represent you in a particular manner (an "engagement letter") you should not send to us any confidential information about any such matter. After we have undertaken representation of you concerning a matter, you will be our client, and we may thereafter exchange confidential information freely.

Thank you for your interest in WilmerHale.