Sidney actually broke into show business as a five-year old, playing sidekick to Tom Mix in the silent film "The Littlest Cowboy" (1921). But he did not pursue acting as a child. Instead, at age 18, Sidney went to work at MGM, first as a messenger boy, then as a sound technician and film editor. Still a teenager, he graduated to directing "Our Gang" comedies, and, at the age of 20, was put in charge of directing all of MGM's screen tests. He was also directing short films, including "Third Dimensional Murder" (1937), which experimented with the 3-D technique (which would later be in vogue during the 1950s), as well as the back to back Oscar-winners "Quicker'n a Wink" (1940) and "Of Pups and Puzzles" (1941). In 1941, Sidney was handed his first feature film directing assignment, "Free and Easy," a lackluster Robert Cummings vehicle. He went on to direct Esther Williams in her first starring vehicle, "Bathing Beauties" (1944), and helped pioneer the combination of live action and animation in "Anchors Aweigh" (1945), notably in the now classic sequence in which Gene Kelly dances with a cartoon Jerry the Mouse. The animated character was created by the animation team of Joseph Barbera and William Hanna and the film marked the start of a long association between Sidney and the duo which would later include a five-year (1961-66) stint as president of the independent Hanna-Barbera Productions.Sidney helped to consolidate the stardom of Judy Garland with "The Harvey Girls" (1946) and he had a success with an all-star version of "The Three Musketeers" (1948) Among his other notable features are "Annie Get Your Gun" (1950), with Betty Hutton in the title role, the 1951 color remake of "Show Boat" and "Kiss Me Kate" (1953) which teamed Kathryn Grayson and Howard Keel and provided Ann Miller with one of her best screen roles. Late in the 50s, with MGM collapsing with the end of the studio system and lavish musicals a thing of the part, Sidney moved to Columbia as a producer as well as director. He served in both capacities on the middling biopic "Jeanne Eagels" (1957), with a miscast Kim Novak in the title role. He fared better with the screen version of the hit Broadway musical "Bye Bye Birdie" (1962), with Ann-Margret, Janet Leigh and Dick Van Dyke. Sidney's screen directing career ended with the unsuccessful musical "Half of Sixpence" (1968). Sidney had occasionally worked on the small screen, including producing the 1964 Academy Awards telecast. He earned an Emmy nomination for directing and producing the United Nations-inspired film "Who Has Seen the Wind?" (ABC, 1965), in which the audience follows a refugee family as it seeks to reach America on a steamer. Still alive and nimble long after many of his contemporaries were not, Sidney participated in American Movie Classics' "Unscripted Hollywood" chat programs, sharing recollections with other stars, such as Betty Garrett and June Allyson. He and his second wife also hosted a local Los Angeles cable show devoted to films, "Reel to Reel."