LeRoy worked in costumes, processing labs and as a camera assistant until he became a gag writer and actor in silent films. His first directing job was in 1927's No Place to Go. When his movies made lots of money without costing too much, he became well-received in the movie business.
In 1930 he directed the gangster epic Little Caesar, and his career was made. In 1938 he was chosen as head of production at MGM. It was his doing that the studio made The Wizard of Oz. He was responsible for discovering Clark Gable, Loretta Young, Robert Mitchum and Lana Turner.
In the 1950s LeRoy directed such musicals as Lovely to Look At, Million Dollar Mermaid, Latin Lovers and Rose Marie. He moved to Warner Brothers, where he was responsible for such famous films as Mister Roberts, The Bad Seed, No Time for Sergeants, The FBI Story and Gypsy.
He was nominated in 1943 for Best Director for Random Harvest. and also in 1940 as the producer of The Wizard of Oz. In addition, he received an honorary Oscar in 1946 for The House I Live In, "for tolerance short subject", and the Irving G. Thalberg Memorial Award in 1976.
LeRoy has a star on the Hollywood Walk of Fame at 1560 Vine Street.