Professor Lupu joined the law school in 1990. After graduating from law school, where he was case editor of the Harvard Law Review, he practiced law with the Boston firm of Hill & Barlow and then joined the law faculty at Boston University, where he taught from 1973 to 1989. During that time, he also served as a visiting professor at Northeastern University and at the University of California, Berkeley. In 1989–90, he was the professor-in-residence on the Appellate Staff of the Civil Division of the U.S. Department of Justice.
Professor Lupu is a nationally recognized scholar in constitutional law, with an emphasis in his writings on the religion clauses of the First Amendment. Together with his colleague Professor Robert Tuttle, Professor Lupu is the co-author of Secular Government, Religious People(Eerdmans Pub. Co., 2014) and many law journal articles.