Mark Harris is head of the White Collar Defense & Investigations Group and co-head of the Appellate Group. Mark is also a former federal prosecutor and law clerk at the U.S. Supreme Court. An experienced white-collar criminal defense lawyer, he represents companies and individuals in their most complex and difficult litigation matters.

Mark’s appellate cases span the gamut from intellectual property and labor relations to constitutional law and administrative law. Since 2017, Mark has represented the Financial Oversight and Management Board for Puerto Rico—the entity created by Congress to oversee Puerto Rico’s bankruptcy, the largest in American history—in dozens of appeals before the U.S. Court of Appeals for the First Circuit. In May 2023, he prevailed before the Supreme Court in an 8-1 decision that recognized the Board’s immunity from suit. He is a Fellow of the American Academy of Appellate Lawyers and a past American Lawyer Litigator of the Week.

Mark also maintains an active criminal docket in cases covering every form of financial crime and civil enforcement, including internal investigations. Clients draw on his experience as a former Assistant U.S. Attorney for the Southern District of New York, where he specialized in fraud cases and tried cases before federal juries. Mark is also a recognized expert on criminal sentencing, as a member of the Board of Editors of the Federal Sentencing Reporter, the leading legal journal devoted to the study of sentencing law and policy, for over 25 years.

Mark is the editor and lead author of Principles of Appellate Litigation: A Guide to Modern Practice (PLI Press), a comprehensive treatise on appellate practice, updated every year, which has been described as “invaluable,” “the product of deep experience and keen insights,” and “a superior appellate practice hornbook.”

He has lectured on both criminal law and appellate practice before the International Bar Association, the National Association of Criminal Defense Lawyers, PLI, and the ABA Sections of Litigation, Criminal Law, and Employment and Labor Law. Mark has been interviewed by Bloomberg Radio, the National Law Journal, WINS AM-1010, Law360, Legal Times, and other news organizations.

Mark is a former clerk to U.S. Supreme Court Justices John Paul Stevens and Lewis Powell, Jr., and Judge Joel Flaum of the U.S. Court of Appeals for the Seventh Circuit. He is a graduate of Harvard College and Harvard Law School, where he was a member of the Harvard Law Review. He also serves on the Board of Trustees of the National Museum of Mathematics.