Born and raised in Los Angeles, McCarey attended high school with future filmmakers Tay Garnett and David Butler and briefly had a career as an amateur middleweight boxer. While attending law school at USC, he was involved in a freak elevator accident. Taking the $5,000 he collected in damages, he invested in a copper mine that went bust. After graduating, McCarey worked in a law firm in San Francisco and then opened his own short-lived practice in his hometown. With the failure of his law practice, Leo McCarey turned to vaudeville, writing sketches and songs but that too proved futile. Old friend David Butler interceded and introduced him to Tod Browning. Browning hired him as an assistant and McCarey gradually worked his way up from “script boy” to assistant director. The veteran helmer even allowed him to direct Lon Chaney in one sequence of “Outside the Law” (1921) and was instrumental in his hiring to direct Universal's “Society Secrets” (1921). The results were less than stellar, however, and once again McCarey found himself considered a failure.
Leo McCarey was, along with Frank Capra, one of the most popular and successful comedy directors of the pre-World War II era. McCarey’s success endured well after World War II, and like Capra, was still influencing filmmakers in the 1990s. During the 1920s, he went to work for Hal Roach Studios as a gag writer and director and, within two years, was a vice president. It was while at Roach that McCarey teamed Stan Laureland Oliver Hardy together for the first time, thus creating one of the most enduring comedy teams of all time. As a director, he imposed a frantically paced, breakneck speed to comedy which quickly became his trademark in the 1930s. A triple-threat as writer and producer as well as director, McCarey made some of the most inspired comedies of the decade, including The Milky Way, Ruggles of Red Gap, and The Awful Truth, collecting an armload of Academy Awards as a director, writer, and producer in the process. His work also had a serious side; McCarey was a devout Catholic and deeply concerned with social issues which came out in films such as Make Way for Tomorrow (1937), a groundbreaking film about the displaced elderly. During the 1940s, his work became more serious McCarey was concerned with the battles that had yet to be fought for human dignity, after World War II was won but this only seemed to make his work more popular. His share in the profits of Going My Way (1944), starring Bing Crosby and Barry Fitzgerald, gave McCarey the highest reported income in the U.S. for the year 1944, and its follow-up, The Bells of St. Mary’s, which was made by McCarey’s own production company, was equally successful.

Source: Wikipedia.org