Conrad had a long acting career in television from the 1950s to the 1980s. In 1962 he appeared in the television series Car 54, Where Are You? in an uncredited part as a construction worker. In 1963 he played Felton Grimes, the title character and murder victim, in the Perry Mason episode "The Case of the Bigamous Spouse". He played Michael Stivic's Uncle Casimir on All in the Family, and gave bigoted Archie Bunker as good as he got.
In 1972 he appeared together with Richard Crenna and Alain Delon in the French language film Un flic, directed by Jean-Pierre Melville. He also had a memorable role in the 1974 film The Longest Yard, playing Nate Scarboro, a retired NFL tight end (New York Giants) who was also the head coach for the Mean Machine, the team of prisoners put together by Burt Reynolds' character Paul Crewe to play the team of guards (Reynolds himself would later play the role of Scarboro in the 2005 remake starring Adam Sandler).
During the 1976–1977 season of Delvecchio, Conrad was a regular as Lt. Macavan.
Conrad died from urethral cancer in November 1983 during the fourth season of Hill Street Blues. The show's Writers wrote his death into the show.
