Rupp was born in Detroit in 1942. He joined the Eastern Hockey League's Philadelphia Ramblers in 1963–64. He played one game in the NHL, on loan with the Detroit Red Wings in 1963–64 replacing Terry Sawchuk. The Red Wings lost 4–1 to the Toronto Maple Leafs.
He was selected as a member of the US team for the 1964 Winter Olympics in Innsbruck, Austria. During the tournament, Rupp shut out East Germany in an 8–0 victory. This feat was not equalled by a US goaltender until Ray LeBlanc held Germany scoreless in the 1992 Winter Olympics. The US team finished in fifth place.
Rupp switched to the Dayton Gems in the International Hockey League in the 1964–65 season. During the next two seasons, he won the James Norris Memorial Trophy for fewer goals against with teammate John Adams.
He returned to play for the Gems until 1972 when he announced his retirement. However, he returned in 1975–76 playing for the Buffalo Norsemen in the North American Hockey League and with the Gems in 1979–80.
After his retirement from ice hockey, Rupp worked in the financial sector. He died of cancer in February 2006.