Leonard White III was born on December 19, 1949, in Queens, New York City, and heard live jazz as a boy because his father took him to gigs. He taught himself the drums, playing a right-handed kit as a left-hander. In the late 1960s he played New York clubs that included the Aphrodisiac, Slugs and the Gold Lounge, and at the Gold Lounge he played his first gig with the alto saxophonist Jackie McLean, with whom he kept working around Queens through the end of the decade.

That circle led to the session that made his name. In August 1969, at 19, he was one of the drummers on Miles Davis's Bitches Brew, recorded live over three mornings from August 19 to 21 at Columbia's Studio B in New York, alongside Jack DeJohnette, the percussionist Don Alias and a band that included Wayne Shorter, Chick Corea, Joe Zawinul, John McLaughlin and Larry Young. White has described the room as an orchestra with Davis as its conductor, everyone in headphones and nothing overdubbed. In 1970 he played on Freddie Hubbard's Red Clay, and in 1972 he joined Corea's new band Return to Forever and, at about the same time, the Latin-rock group Azteca.

Return to Forever had first cut its third album with Steve Gadd on drums, but Gadd would not give up studio work to tour, and White took the chair and re-recorded Hymn of the Seventh Galaxy (1973, Polydor); the Gadd version was never released. With Corea, Stanley Clarke and, from the next album, guitarist Al Di Meola, he made the quartet's best-known records: Where Have I Known You Before (1974), No Mystery (1975) and Romantic Warrior (1976), the group's first for Columbia, recorded in February 1976 at Caribou Ranch in Colorado and including White's tune "Sorceress." After Romantic Warrior Corea reshaped the band without White and Di Meola, and the quartet era ended in 1977.

White had begun leading his own dates during those years. Venusian Summer (Nemperor, 1975), recorded in June and August 1975 at Electric Lady Studios in New York and in San Francisco, found him drumming, playing keyboards and synthesizers and producing, with Di Meola, the guitarist Larry Coryell, Hubert Laws, the organists Larry Young and Jimmy Smith, and the keyboardists David Sancious and Onaje Allan Gumbs. Big City (1977), a second Nemperor date, brought in Marcus Miller, Herbie Hancock and Earth, Wind & Fire's Verdine White and reached No. 17 on Billboard's jazz albums chart; the Elektra albums The Adventures of Astral Pirates and Streamline followed in 1978. In 1979 he formed the R&B and funk band Twennynine, which made Best of Friends (1979), Twennynine with Lenny White (1980) and Just Like Dreamin' (1981) for Elektra with Larry Dunn co-producing; the single "Peanut Butter" reached No. 3 on Billboard's R&B chart. In 1982 he produced Chaka Khan's Echoes of an Era for Elektra, a set of jazz standards recorded at Mad Hatter Studios in Los Angeles, on which she sang with a band of White, Corea, Clarke, Joe Henderson and Hubbard, and the same band went on to record as the Griffith Park Collection. The Return to Forever quartet also reunited that year for "Compadres" on Corea's Touchstone.

Through the 1980s White worked as a producer and in R&B and funk groups. He produced and co-wrote Bernard Wright's "Who Do You Love" (1985), co-produced Pieces of a Dream's Joyride (1986) with Maurice White, played in the Queens-based funk group Jamaica Boys with Miller and Wright (Warner Bros., 1987 and 1990), and with Miller scored the 1990 film House Party. His jazz leadership returned with a run of albums for Hip Bop Records, Present Tense (1995), Renderers of Spirit (1996) and Edge (1998), and with The Manhattan Project (Blue Note, 1990), his own idea: a live recording made before an audience at Chelsea Studios in New York in 1989, arranged by White and Gil Goldstein, that recast standards with Wayne Shorter, Michel Petrucciani, Clarke and the keyboardists Goldstein and Pete Levin. Hancock Island (Chesky, 2008) was a set of Herbie Hancock tunes with Buster Williams, the pianist George Colligan and the saxophonist Steve Wilson.

Return to Forever came back in 2008, when Corea, Clarke, Di Meola and White toured the United States and Europe and issued the live Returns. In 2009 Corea, Clarke and White toured as an acoustic trio and recorded the live double album Forever (Concord, 2011), which won the Grammy for Best Jazz Instrumental Album in 2012 and a Latin Grammy for Best Instrumental Album. A 2011 tour of the group added Jean-Luc Ponty and the guitarist Frank Gambale, and White kept playing with Corea and Clarke until Corea's death in 2021. White co-produced Clarke's The Stanley Clarke Band (2010), which won the Grammy for Best Contemporary Jazz Album, and led the electric Anomaly (Abstract Logix, 2010) and Lenny White Live (2013). In acoustic jazz he has been a regular partner of Buster Williams, whose own profile lists him as the drummer on most of Williams's leader dates from 1997 onward, and of Wallace Roney, on whose albums Village (1997), No Room for Argument (2000) and A Place in Time (2016) he played, and in 2015 he joined Williams and the pianist Cyrus Chestnut as a trio, recorded on Chestnut's Natural Essence (HighNote, 2016). He has won three Grammys, for No Mystery, The Stanley Clarke Band and Forever, plus the Latin Grammy. As of 2026 New York University lists him as adjunct faculty in jazz studies and percussion studies at its Steinhardt school, and says he also teaches at The New School.

White has been called one of the founding fathers of jazz fusion, and his drumming joins its two halves: the open, conversational time of the bebop and hard-bop drummers he names as models (Kenny Clarke, Max Roach, Art Blakey, Philly Joe Jones, Roy Haynes, Elvin Jones and Tony Williams, to whom he dedicated a piece called "Magnificent Seven") and the heavy backbeat and funk grooves that drove Return to Forever and his own R&B-leaning records. His Return to Forever work shows a drummer at ease with the group's odd meters, unison lines and orchestral dynamics as well as with plain funk. His own albums range from the synthesizer-heavy science-fiction concept of The Adventures of Astral Pirates to the Twennynine dance singles, the funk-jazz of Present Tense and the hard-rocking Anomaly, which All About Jazz's Ian Patterson heard as a rock album with the improvisation of White's early career still audible. A 2018 New York Jazz Workshop interview introduction describes him as moving between straight-ahead jazz, jazz rock, jazz funk, R&B and hip-hop grooves without changing his approach, and he calls himself a bridge between his generation and younger players. He plays signature Epoch cymbals from Istanbul Agop and Vic Firth sticks.