From 1966 to 1987, Boudin practiced law at Covington & Burling, a Washington, D.C., law firm.[4] He worked as a visiting professor at Harvard Law School from 1982 to 1983, and then as a lecturer there from 1983 to 1998. He then served in President Reagan's Justice Department as a deputy assistant United States Attorney General of the Antitrust Division from 1987 to 1990.[6]
Two months later, on March 20, 1992, President Bush nominated Boudin to an appellate judgeship on the United States Court of Appeals for the First Circuit, headquartered in Boston, to the seat vacated when Judge Levin H. Campbell assumed senior status. He was confirmed by the Senate on May 21, 1992, and received his commission on May 26, 1992.[6] Boudin served as Chief Judge of the First Circuit from 2001 to 2008. He assumed senior status on June 1, 2013.[7][6] He retired from service on December 15, 2021.[6]
The New York Times stated that Boudin was "not easy to pigeonhole ideologically".[4] He was described by some as a conservative[3][2] and by others as a centrist.[2][8] In 2012, Boudin penned a decision holding the Defense of Marriage Act, a federal law defining marriage as an opposite-sex union, unconstitutional.[9] Boudin was widely regarded as having a brilliant legal mind.[2][4][8]