Stevens was born in Chicago, Illinois. He married Maryan Mulholland, and has four children: John Joseph (deceased), Kathryn, Elizabeth Jane, and Susan Roberta. He received an A.B. from the University of Chicago, and a J.D. from Northwestern University School of Law. He served in the United States Navy from 1942-1945, and was a law clerk to Justice Wiley Rutledge of the Supreme Court of the United States during the 1947 Term. He was admitted to law practice in Illinois in 1949. He was Associate Counsel to the Subcommittee on the Study of Monopoly Power of the Judiciary Committee of the U.S. House of Representatives, 1951-1952, and a member of the Attorney General's National Committee to Study Antitrust Law, 1953-1955. He was Second Vice President of the Chicago Bar Association in 1970. From November 2, 1970 to 1975, he served as a Judge of the United States Court of Appeals for the Seventh Circuit, nominated by by President Nixon. President Ford then nominated him as an Associate Justice of the Supreme Court, and he took his seat December 19, 1975.