Milton Rosen played the violin from an early age and was later trained in orchestration and composition at the Institute of Musical Art in New York, where he worked with Italian composer Pietro Floridia and the Russian emigre conductor Vladimir Bakaleinikoff. He composed several classical pieces (including "A Columnist Suite for Violin & Piano") during the 1930's, which were widely performed by notable symphony orchestras in Boston, Pittsburgh, Cincinatti, and at the Hollywood Bowl. Rosen also worked in radio and musical theatre, primarily as orchestrator and arranger. In 1939, he joined the music department at Universal and became a member of ASCAP two years later.

Rosen remained under contract with Universal (except for a brief stint at Fox in 1948), from 1943 until 1973. During his tenure, he wrote more than 150 songs and contributed, either as arranger, conductor or musical supervisor to dozens of the studio's often colourful, escapist extravaganzas. After 1950, Rosen held the position of assistant to the head of the music department at Universal.