Rotunda joined Chapman in 2008. Prior to coming to Chapman, he was a university professor and professor of law at George Mason University School of Law, joining George Mason in 2002. Before that, he was the Albert E. Jenner, Jr. Professor of Law at the University of Illinois. He joined the University of Illinois faculty in 1974 after clerking for Judge Walter R. Mansfield of the United States Court of Appeals for the Second Circuit, practicing law in Washington, D.C., and serving as assistant majority counsel for the Watergate Committee.

Rotunda is a magna cum laude graduate of Harvard College and a magna cum laude graduate of Harvard Law School, where he was a member of Harvard Law Review. He is the author or co-author of a number of widely used course books and treatises on professional responsibility and constitutional law. He is also the author of several other books and more than 200 articles in various law reviews, journals, newspapers, and books in the United States and in Europe. His works have been translated into French, German, Romanian, Czech, Russian, and Korean. These books and articles have been cited more than 1,000 times by state and federal courts at every level, from trial courts to the U.S. Supreme Court. He has been interviewed on radio and television on legal issues, both in this country and abroad.

In 1993, Rotunda was the Constitutional Law Adviser to the Supreme National Council of Cambodia and assisted that country in writing its first democratic constitution. He has consulted with various new democracies in Eastern Europe and the former Soviet Union, including Moldova, Romania, and Ukraine, on their proposed constitutions and judicial codes. He chaired the subcommittee that drafted the American Bar Association's Model Rules for Lawyer Disciplinary Enforcement; is a member of the Publications Board of the A.B.A. Center for Professional Responsibility since 1994; was a member of the A.B.A. Standing Committee on Professional Discipline (1991–1997); and was liaison to the A.B.A. Standing Committee on Ethics and Professional Responsibility (1994–1997). He was a Fulbright Professor in Venezuela in 1986 and a Fulbright Research Scholar in Italy in 1981. In 1996 he assisted the Czech Republic in drafting the first Rules of Ethics for lawyers in that country. During the spring 1999 semester, he was visiting professor at the University of Alabama School of Law, holding the John S. Stone Endowed Chair of Law. During the summer and fall of 2000, he was the Visiting Senior Fellow in Constitutional Studies at the Cato Institute, in Washington, D.C. In the fall of 2001, he was visiting professor at George Mason University School of Law. During November–December 2002, he was Visiting Scholar, Katholieke Universiteit Leuven, Faculty of Law, Leuven, Belgium. In May 2004 and December 2005, he was visiting lecturer at the Institute of Law and Economics, Institut für Recht und Ökonomik, at the University of Hamburg. From early June 2004 to May 2005, he was the special counsel to the General Counsel of the Department of Defense. He was on the Panel of Contributing Editors that produced Black's Law Dictionary® (Thompson-West, 8th ed. 2004). From 2005–2006, he was a member of the Task Force on Judicial Functions of the Commission on Virginia Courts in the 21st Century: To Benefit All, to Exclude None. In May 2000, American Law Media, publisher of The American Lawyer, National Law Journal, and the Legal Times picked Professor Rotunda as one of the 10 most influential Illinois lawyers. Also in 2000, a lengthy study that the University of Chicago Press published, which sought to determine the influence, productivity, and reputations of law professors over the last several decades, listed Professor Rotunda as the 17th highest in the nation. The 2002–2003 New Educational Quality Ranking of U.S. Law Schools (EQR) ranks Professor Rotunda as the 11th most cited of all law faculty in the United States. See http://www.leiterrankings.com/faculty/2002faculty_impact_cites.shtml. In July 2007, he was one of the main speakers at the International Judicial Conference hosted by the United States Embassy, the Supreme Court of Latvia, and the Latvian Ministry of Justice. The other main speakers were Justice Samuel Alito, the president of Latvia, the prime minister of Latvia, the chief justice of Latvia, and the minister of justice of Latvia.