Michel Jean Legrand was born February 24, 1932, in Bécon-les-Bruyères, in the Paris suburbs, to conductor and composer Raymond Legrand and Marcelle Der-Mikaëlian, whose brother was the bandleader Jacques Hélian. His parents separated when he was three, and he later said the family piano became "my only friend, my only love" as he taught himself to pick out melodies he had heard on the radio. At ten he entered the Paris Conservatoire, where he studied under Nadia Boulanger, Henri Challan, and Noël Gallon and graduated with top honors as both a pianist and a composer. His sister, Christiane Legrand, went on to a career as a jazz vocalist, later a member of the Swingle Singers. The turn toward jazz came in 1947, when the teenage Legrand heard Dizzy Gillespie play a concert in Paris: "I was ecstatic," he recalled, describing the discovery of "another world, another planet."

Out of the Conservatoire, Legrand became musical director and accompanist to Maurice Chevalier, a job that took him on tour to the United States for the first time in the early 1950s. His own 1954 orchestral debut, the mood album I Love Paris, became a surprise hit and established him commercially, but it was a 1958 trip back to New York, made possible by his Columbia Records contract, that produced his defining jazz statement. Over three sessions on June 25, 27, and 30, 1958, Legrand assembled and conducted an extraordinary cross-section of the era's leading jazzmen for Legrand Jazz: Miles Davis, John Coltrane, Bill Evans, Ben Webster, Paul Chambers, Herbie Mann, Phil Woods, Hank Jones, Donald Byrd, and Art Farmer among them, reimagining eleven jazz standards through his own dense, classically trained orchestral arrangements. Critic Leonard Feather later called it "unquestionably one of the most successful orchestral jazz albums of all time."

Legrand kept a working jazz career going alongside his fast-growing reputation as a film composer through the 1960s. In 1959 he recorded the trio date Paris Jazz Piano in Paris with bassist Guy Pedersen and drummer Gus Wallez, a set of Paris-themed standards issued in France on Philips and released in the United States the following year, retitled Legrand Piano, on Columbia. Nearly a decade later, in 1968, he cut At Shelly's Manne-Hole for Verve, a live trio session recorded at Shelly Manne's Hollywood club with bassist Ray Brown and drummer Shelly Manne, several of its pieces improvised on the spot; a period reviewer singled out Legrand's own piano work on "Another Blues" and "Ray's Riff."

The 1970s brought a run of high-profile jazz collaborations built around Legrand's arranging. In 1972 he arranged and conducted Sarah Vaughan with Michel Legrand for Mainstream, built largely from songs he had written with lyricists Alan and Marilyn Bergman, and won the Grammy Award for Best Instrumental Arrangement Accompanying Vocalist(s) for "What Are You Doing the Rest of Your Life?" from that record. The same year he composed, arranged, and played on Stan Getz's Communications '72 for Verve. In 1975 he arranged Lena Horne's Lena & Michel for RCA and, in the same year, orchestrated and conducted Phil Woods's Images, which won Grammy Awards for Best Instrumental Composition and Best Jazz Performance by a Big Band. He led his own big band on Le Jazz Grand, recorded at RCA Studios in New York in March 1978 and released the following year on Gryphon, built around a jazz suite drawn from his own soundtrack to Les Routes du Sud and featuring septet tracks with Phil Woods, trumpeter Jon Faddis, and baritone saxophonist Gerry Mulligan.

Legrand's jazz output continued into the 1980s and 1990s even as his soundtrack work reached its commercial peak. He recorded the septet album After the Rain in New York in May 1982 (released 1983, Pablo) again with Phil Woods, alongside Zoot Sims, trumpeter Joe Wilder, guitarist Gene Bertoncini, bassist Ron Carter, and drummer Grady Tate. In 1991 he reunited with Miles Davis, who also appeared on screen, for the soundtrack to the film Dingo, their first joint project since Legrand Jazz thirty-three years earlier. In 1992 he recorded the trio album Autumn in Paris and, that May in Paris, Legrand Grappelli for Verve with violinist Stéphane Grappelli, a session that also featured trumpeter Stéphane Belmondo, who had joined Legrand's big band around 1990 and was on stage for the pair's first meeting at the Paris Olympia earlier that year. He led an all-star sextet including trumpeter Arturo Sandoval, trombonist Bill Watrous, and flutist Hubert Laws on Michel Plays Legrand, recorded in Hollywood in September 1993 and released in 1995, and followed it with the trio date The Warm Shade of Memory (recorded March 1995, released 1996), which added a guest turn from harmonica player Toots Thielemans.

In 2002 Legrand released Michel Legrand by Michel Legrand, his first solo piano recording devoted entirely to his own compositions. Alongside this steady jazz output ran the far more widely known career for which he is best remembered outside jazz circles: scores for Jacques Demy's The Umbrellas of Cherbourg (1964) and The Young Girls of Rochefort (1966), for directors including Jean-Luc Godard, Agnès Varda, and Orson Welles, and, from the late 1960s, a long run of Hollywood work that brought him three Academy Awards, for the song "The Windmills of Your Mind" from The Thomas Crown Affair (1968), the score for Summer of '42 (1971), and the adapted score for Yentl (1983), plus multiple Grammy Awards. He remained active into his final years, scoring Peter Bogdanovich's 2018 completion of Orson Welles's long-unfinished The Other Side of the Wind. Michel Legrand died January 26, 2019, in Neuilly-sur-Seine, France, at eighty-six, after being hospitalized with a pulmonary infection.

Legrand's jazz identity was that of an arranger-pianist whose conservatory training shaped everything he touched: dense, harmonically sophisticated big-band and chamber-jazz voicings built to frame world-class soloists rather than compete with them. Legrand Jazz remains the clearest statement of that approach, pairing hard-bop-caliber improvisers with orchestrations a jazz combo alone could not produce; reviewing the album decades later, All About Jazz found "Legrand's genuine love of jazz" and "his commitment to sleek, modern swing" self-evident, while noting the results lacked the "legendary status" of Gil Evans's comparable work with Miles Davis, a touch of what the reviewer called Gallic insouciance. As a player, Legrand favored an elegant, harmonically alert touch rather than a percussive one, evident on his trio recordings and singled out by critics on At Shelly's Manne-Hole. He kept returning to jazz throughout a career that made him vastly more famous as a film composer, treating it not as a sideline but as a working practice he never abandoned, from a 1947 Dizzy Gillespie concert that redirected his ear as a teenager to a solo piano album of his own songbook released when he was seventy.