After graduating from Woodbury College in Los Angeles, California, he joined his father in the garment business and worked his way up from office boy to vice president.
Denning portrayed George Cooper, the husband of Lucille Ball, on CBS Radio's "My Favorite Husband" (1948-1951). The series was such a success that CBS executives offered Ball a TV deal with Denning, but she refused, insisting on husband Desi Arnaz as her TV husband.
During World War II, he enlisted in the U.S. Navy and served on a submarine as Yeoman 1st Class.
He had a daughter with his first wife, Evelyn Ankers.
His character's name on CBS Radio's "My Favorite Husband" was changed from George Cugat to George Cooper later in 1948.
Interviewed in Tom Weaver's book "They Fought in the Creature Features" (McFarland & Co., 1995).