 As a law student, he was editor-in-chief of the "Yale Law Journal" for 1951–1952 and he clerked for U.S. Supreme Court Justice Hugo L. Black during the 1953-1954 term.During this period he also became a friend of Justice William O. Douglas, as he recounts in his autobiography.Prior to his academic career he worked for six years as a lawyer at the white-shoe firms Cravath, Swaine & Moore in New York and Arnold & Porter in Washington, D.C.

Reich was a professor at Yale Law School from 1960-1974.