Professor R. Michael Cassidy teaches and writes in the areas of Criminal Law, Evidence, and Professional Responsibility. He is considered an expert on the subject of prosecutorial ethics, and provides training nationally to public sector attorneys on their responsibilities under the Rules of Professional Conduct. He is quoted frequently on subjects relating to criminal law and ethics in the New York Times, the Boston Globe, and the Boston Herald.

During his extensive career as a government lawyer, Professor Cassidy served as Chief of the Criminal Bureau in the Massachusetts Attorney General’s Office under then Attorney General Scott Harshbarger. He also served as a member of the Massachusetts State Ethics Commission, as Editor-in-Chief of the Massachusetts Law Review, as a member of the Governor's Commission on Corrections Reform, as a hearing officer for the Massachusetts Board of Bar Overseers, as a member of the Criminal Justice Section Council of the Boston Bar Association, as an Advisor to the National District Attorneys' Association, as a member of the Massachusetts Judicial Nominating Commission, and as a legal consultant to the Department of Justice on issues of police misconduct and prosecutorial ethics.

Professor Cassidy was recently appointed to serve a three year term on the Supreme Judicial Court's Standing Advisory Committee on the Rules of Professional Conduct. Professor Cassidy was elected to the American Law Institute in 2012.