A stage actor as a teenager, Lamont began acting in films in 1919. Three years later he was directing comedy two-reelers, and over the '20s he helmed shorts for Mack Sennett and Al Christie. He moved to features in 1934, and directed numerous films over the next twenty years. Lamont specialized in comedy, most notably eight Abbott and Costello films in the late '40s and early '50s, including Abbott and Costello Meet Captain Kid, co-starring Charles Laughton, and Abbott and Costello Meet the Invisible Man.