Born Martin Harris Calinieff in Philadelphia, Pennsylvania, Callan began his career as Mickey Calin, and it was with this name he appeared on Broadway in The Boy Friend (1954), Catch a Star (1955), and West Side Story (1957).
Callan's film career began in 1959 with roles in two films, They Came to Cordura and The Flying Fontaines. Although he was unable to reprise his West Side Story role of Riff in the film version due to his contract with Columbia Pictures, he did dance in the film Gidget Goes Hawaiian (1961). His screen credits include The Interns, The New Interns,with Barbara Eden, Mysterious Island (1961), Cat Ballou, Leprechaun 3 and Stuck on You.
In 1966, Callan landed the lead role of Peter Christopher in the sitcom Occasional Wife. Callan and Patricia Harty, the actress who played his "occasional wife" in the series, fell in love in real life and were married for several years.
Additional television credits include That Girl, The Name of the Game, The Mary Tyler Moore Show, Ironside, Marcus Welby, M.D., McMillan & Wife, Barnaby Jones, Quincy M.E., Charlie's Angels, Simon and Simon, Fantasy Island, four episodes of Murder, She Wrote, and eight episodes of ''Love, American Style.