Leonard Rosenman was born in Brooklyn, New York. After service in the Pacific with the United States Army Air Forces in World War II, he earned a bachelor’s degree in music from the University of California, Berkeley. He also studied composition with Arnold Schoenberg, Roger Sessions and Luigi Dallapiccola. Amongst Rosenman’s earliest film work was the scores for James Dean movies East of Eden (1955) and Rebel Without a Cause (1955). Rosenman had lived together with Dean whom he gave piano lessons to and it was Dean who introduced him to the director Elia Kazan. Dean also lobbied George Stevens to score Giant, but Stevens preferred the more traditional Dimitri Tiomkin. Leonard Rosenman remarked “The year I did my first film, I had five major performances in New York,” however. “The minute I did my first film, I didn’t have a performance there for 20 years. They would never say, ‘I don’t like them’. They wouldn’t look at them.” He composed the score for Vincente Minnelli’s The Cobweb (1955) regarded as the first major Hollywood score to be written in a 12-note (properly called 12-tone) manner. His avant-garde music was used for Martin Ritt’s Edge of the City (1956) and John Frankenheimer’s The Young Stranger (1957). He composed scores for war films such as William Wellman’s biographical Lafayette Escadrille (1958), Lewis Milestone’s Pork Chop Hill (1959), Delbert Mann’s The Outsider (1961), Don Siegel’s Hell is for Heroes (1962) and the Combat! television series (1962). He wrote incidental music for such television series as Law of the Plainsman, The Defenders, The Twilight Zone, Gibbsville and Marcus Welby, M.D..

He went on to compose George Cukor’s The Chapman Report then Fantastic Voyage (1966) where he rejected producer Saul David’s instructions. Leonard Rosenman stated “A producer asked me to write a jazz score, and I asked him why. He said he wanted the picture to be the first hip science fiction movie. I said that’s a great idea for an advertising agency, but it doesn’t fit the film.” He provided scores to science fiction films such as Beneath the Planet of the Apes (1970) and the first, animated adaptation of The Lord of the Rings (1978), Cross Creek (1983) and Star Trek IV: The Voyage Home (1986). In the 1970s he composed Bass Concerto Chamber Music 4 for bassist Buell Neidlinger and four string quartets with a second bass. In 1995 Nonesuch Records issued an album of music from both East of Eden and Rebel Without A Cause, played by the London Sinfonietta conducted by John Adams. In his 70s Rosenman was diagnosed with Frontotemporal dementia, a degenerative brain condition with symptoms similar to Alzheimer’s disease. He died March 4, 2008, of a heart attack at the Motion Picture & Television Country House and Hospital in Woodland Hills, Los Angeles, California.