After school, Chaplin joined the ASCAP and started out penning tunes for the theatre, vaudeville and for New York's famous songwriting district, Tin Pan Alley.
While in New York, Chaplin teamed with Sammy Cahn to compose original songs for Vitaphone movie shorts, filmed in Brooklyn by Warner Brothers.
In the late 1940s, Chaplin moved to MGM to work on a long string of films including On the Town (1949), Kiss Me Kate (1953), High Society (1956) and Merry Andrew (1958).
He won Academy Awards for his work on the scores of Seven Brides for Seven Brothers, An American in Paris and West Side Story as well as nominations for Kiss Me Kate and High Society.
He had worked with and was friends with most of the major songwriters and performers of his era, such as Cole Porter, Ira Gershwin, Al Jolson, Leonard Bernstein, Judy Garland, Gene Kelly, Phil Silvers, Julie Andrews, Frank Sinatra and others.