From 1960 to 1965, Selin was a research engineer at the RAND Corporation, working on national security issues and statistical communication theory. In 1965, Selin went to work for the Office of the Secretary of Defense, one of Robert S. McNamara's Whiz Kids. From 1965 to 1970, Selin worked for McNamara, becoming Acting Assistant Secretary of Defense for Systems Analysis by the end of that period. While serving in this capacity, Selin represented the Office of the Secretary of Defense at the commissioning of the USS Knox (FF-1052).[2] He received the Department of Defense Distinguished Civilian Service Medal in 1970.[3]
In 1970, Selin and several DOD colleagues co-founded American Management Systems, a technology and management consulting firm. Selin served as chief executive officer from the company's founding to the late 1980s.
On July 1, 1991, Selin became chairman of the Nuclear Regulatory Commission, serving in that capacity until he resigned on June 30, 1995. Selin was sworn in by outgoing NRC chairman Kenneth Monroe Carr and also had a ceremonial swearing-in ceremony at which Vice President Dan Quayle presided and Supreme Court Justice Sandra Day O'Connor administered the oath. Selin was founding chairman of the board of the Smithsonian Institution's National Museum of American History.