Gerry Mulligan grew up in Philadelphia and first learned piano, which he played occasionally. While in his teens, he wrote arrangements for Johnny Warrington's radio band (1944) and played reed instruments professionally. After moving to New York in 1946, he joined Gene Krupa's big band as staff arranger, attracting attention with his Disc Jockey Jump (1947). He then became involved with the nascent cool-jazz movement in New York, taking part in the performances (1948) and recording sessions (1949-50) of Miles Davis' nonet and contributing scores to the big bands of Elliot Lawrence and Claude Thornhill. By this time, he was specializing in baritone saxophone and playing in groups with Kai Winding and others. He also wrote scores for Stan Kenton's band and recorded with his own tentet (1951), which was modeled on Davis's ensemble.
In 1952, Mulligan, then based in Los Angeles, formed his first piano-less quartet, with Chet Baker on trumpet. The group was instantaneously successful and brought Baker and Mulligan international acclaim. Mulligan led a new tentet and various versions of the quartet throughout the mid-1950s. He made a sensational appearance at the Salle Pleyel in Paris in 1954 and began dominating jazz opinion polls for his instrument. In 1960, he organized his own 13-piece concert jazz band with which he toured Europe in that year and Japan in 1964. After it disbanded, he became an active sideman, working often with Dave Brubeck (1968-72) and as a freelance arranger for other jazz groups. He formed a new 14-piece big band, the Age of Steam, in 1972, and was artist-in-residence at Miami University in 1974.