Warner's career in public service began with his enlistment in the United States Navy in January 1945, where he served until the following year, leaving as a Petty Officer 3rd Class. He then attended Washington and Lee University, graduating in 1949, then went to the University of Virginia Law School.
He joined the United States Marine Corps in October 1950, after the outbreak of the Korean War, and served in Korea as a ground officer with the 1st Marine Air Wing. He continued in the Marine Corp Reserve after the war, eventually reaching the rank of Captain.
After resuming his studies and graduating from Virginia, he became a law clerk (1953) to Chief Judge E. Barrett Prettyman of the US Circuit Court of Appeals, then an assistant US attorney in 1956, and then entered private law practice in 1960.
In February 1969 he was appointed Under Secretary of the Navy by the Nixon administration, then on May 4, 1972 succeeded John H. Chafee as Secretary of the Navy. During this period he participated in the Law of the Sea talks, and negotiated the Incidents at Sea Executive Agreement with the Soviet Union.
He married Elizabeth Taylor on December 4, 1976, but they were divorced November 7, 1982. He had earlier (when?) married and divorced heiress Catherine Mellon.
Warner entered electoral politics for the first time in the 1978 election, winning a Senate seat that he has held since. Committee memberships have included the Environment and Public Works Committee, the Senate Committee on Health, Education, Labor, and Pensions, and the Select Committee on Intelligence, and most importantly he is the chairman of the Senate Armed Services Committee.