Mark Cahn focused his practice on government and internal investigations, enforcement proceedings and litigation involving financial institutions, individuals and public companies. Over the course of his career, he represented clients in internal corporate investigations, enforcement proceedings involving the Securities and Exchange Commission (SEC), FINRA and other regulatory bodies, and federal and state court litigation. His matters involved a broad range of issues, including financial reporting, regulatory compliance, accounting and disclosure inquiries, securities and other financial fraud, and insider trading. He first joined WilmerHale in 1988 and later rejoined the firm after serving as General Counsel of the SEC from 2011 to 2013. He retired from the firm in 2024.

As General Counsel of the SEC, Mr. Cahn provided legal advice to the Commission and its Divisions on enforcement, litigation and regulatory matters, advised on the implementation of rulemakings, and played a key role in the development of the SEC's Whistleblower Program. He previously served as Deputy General Counsel for Litigation and Adjudication at the SEC from 2009 to 2011, advising the Commission on enforcement recommendations and overseeing the litigation, appellate and adjudication functions of the Office of the General Counsel. He also spoke to professional and industry groups on securities enforcement and litigation topics and served on the Executive Council of the Securities Law Committee of the Federal Bar Association and the Board of Trustees of the SEC Historical Society