Born in Poughkeepsie, New York in 1907,[2] Harmon produced Broadway plays throughout the 1930s (1931-1937).[3] Harmon was one of many members of the Group Theatre to become involved with movie production.[4] He married artist Lily Harmon (née Perlmutter) in 1934; they divorced in 1940.[5] He worked with movies from the 1940s to the 1960s. In 1959, he co-founded the Theatre Group at the University of California at Los Angeles with John Houseman and Robert Ryan.[6]
Harmon, with Ryan and others, initiated the Oakwood School in California in 1951.[7]
During retirement, Harmon was active in the cultural life of Palm Springs, California; he was the first director emeritus of the McCallum Theatre in Palm Desert.[8] The Desert Theatre League's Sidney Harmon Award honored members "in recognition of the advancement of theatrical excellence both on and off the stage".[9]