Kenneth Barron is born June 9, 1943, in Philadelphia, the youngest of five children in a household where his mother requires every child to take piano. He starts at six and dislikes it at first. His eldest brother, the tenor saxophonist Bill Barron, is seventeen years older and already working professionally, and it is Bill who begins asking him questions about music once he discovers his younger brother sitting at the piano playing blues chords by ear. Barron studies with Vera Bryant, a sister of the pianist Ray Bryant and the mother of guitarist Kevin Eubanks, trombonist Robin Eubanks and trumpeter Duane Eubanks. At fifteen he plays briefly in Mel Melvin's Philadelphia orchestra, a band that also carries his brother on tenor. In 1959, still in high school, he takes local gigs with Jimmy Heath, and two months before graduating he plays a night with Yusef Lateef; a few days after the ceremony he is on the road with Lateef for a week. His first recording comes at seventeen, on his brother's The Tenor Stylings of Bill Barron, cut at Medallion Studios in Newark on February 21, 1961, with Ted Curson on trumpet, Jimmy Garrison on bass and Frankie Dunlop on drums.

Barron moves to New York in 1961. James Moody hears him at the Five Spot and hires him on the spot, and in the same year he works briefly with Lou Donaldson, Roy Haynes and Lee Morgan. In 1962 he joins Dizzy Gillespie's quintet at nineteen and stays through 1966, touring internationally and recording Something Old, Something New (Philips, 1963), the score to Shirley Clarke's film The Cool World (Philips, 1964), Jambo Caribe (Limelight, recorded in Chicago on November 4 to 6, 1964, with Moody, Chris White and Rudy Collins) and The Melody Lingers On (Limelight, 1966). Gillespie's book gives him a working command of Latin and Caribbean rhythm that never leaves his playing. He is also briefly a member of the Jazztet around 1962, though the group never records with him.

After Gillespie he works with Stanley Turrentine and then spends three years with Freddie Hubbard, whose High Blues Pressure (Atlantic) he cuts across sessions on November 13, 1967, and January 10, 1968, playing on five of its six pieces. He records The Kicker and Tetragon with Joe Henderson for Milestone in 1967, and takes engagements with Milt Jackson and Buddy Rich, appearing on the drummer's Very Live at Buddy's Place (Groove Merchant, 1974) on five of its six tracks. In 1970 he works as accompanist and arranger for the singer Esther Marrow, and the following year he rejoins Yusef Lateef for close to five years, a stretch he credits with opening up his improvising: The Gentle Giant (Atlantic, 1972), Part of the Search (1974) and the live double album 10 Years Hence, taped at San Francisco's Keystone Korner on July 5 and 6, 1974. His own first leader date, Sunset to Dawn, is recorded at RCA Studio in New York on April 2, 1973, and issued by Muse.

Two long institutional commitments begin in this period. Barron joins the music faculty at Rutgers University in 1974 and teaches there until 2000, mentoring David Sanchez, Terence Blanchard and the guitarist Peter Bernstein among many others, and he takes a B.A. in arts from Empire State College in 1978. In 1977 he co-founds Sphere with bassist Buster Williams, drummer Ben Riley and saxophonist Charlie Rouse, the last two veterans of Thelonious Monk's own bands; the group's first album, Four in One, is recorded on February 17, 1982, the day Monk dies. Sphere runs through Bird Songs (Verve, 1988), disbands after Rouse's death that year, and reunites a decade later with Gary Bartz in the saxophone chair. Overlapping it is the association that reaches the widest audience: from 1986 Barron is Stan Getz's pianist, recording Voyage (BlackHawk, March 9, 1986), the Copenhagen concert that yields both Anniversary! and Serenity (July 6, 1987), the 1989 A&M sessions later issued as Bossas & Ballads: The Lost Sessions, and the four nights at the Café Montmartre in March 1991 that become People Time, Getz's last recording. Getz calls him his favorite pianist of all time.

The leader catalogue grows steadily across small independent labels through the 1970s and 1980s (Muse, Xanadu, Enja, Criss Cross Jazz, Reservoir, Uptown, Baystate) before Verve signs him in 1992 and releases Sambao, Other Places, Wanton Spirit, Things Unseen, Night and the City, Spirit Song and Freefall over the following decade. Sunnyside issues Canta Brasil (2002), Images (2004) and The Traveler (2008); Impulse! releases the duo record The Art of Conversation with Dave Holland in 2014 and Book of Intuition in 2016; Blue Note releases Concentric Circles in 2018. Since 2015 his working trio has been bassist Kiyoshi Kitagawa and drummer Johnathan Blake. He has composed more than fifty pieces, the best known of them "Voyage," which other musicians have recorded upwards of seventy-five times, and he has contributed to the scores of Spike Lee's Do the Right Thing (1989) and Malcolm X (1992).

Barron is named an NEA Jazz Master in 2010, having been inducted into the American Jazz Hall of Fame in 2005 and elected a Fellow of the American Academy of Arts and Sciences in 2009. Berklee College of Music gives him an honorary doctorate in 2010, and DownBeat's readers elect him to its Jazz Hall of Fame in 2022. His fourteenth Grammy nomination arrives in 2024 for Beyond This Place, an Artwork Records date with Immanuel Wilkins on alto saxophone and Steve Nelson on vibraphone. He now teaches at the Juilliard School, continues to tour solo and with the trio, and keeps recording: the solo Paris concert The Source (2023), the vocal project Songbook (2025), and Stars (2026, Newvelle Records), a vinyl-only trio session led by bassist Martin Wind with clarinetist Anat Cohen and drummer Matt Wilson.

Barron names Hank Jones and Tommy Flanagan as his principal models, and what he took from them was touch and phrasing rather than vocabulary: he describes their lines as elastic, "like a rubber band," never rigid, an ebb and flow he has spent a career refining. He also cites Wynton Kelly, his fellow Philadelphian McCoy Tyner and Herbie Hancock. The result is a mainstream post-bop language of unusual balance: dense two-handed voicings that never crowd a soloist, a legato right hand that carries a melody the way a horn player would, and a rhythmic elasticity in ballads that made him the accompanist of choice for singers including Abbey Lincoln, Helen Merrill, Dianne Reeves and Ann Hampton Callaway. The five years in Gillespie's band left him fluent in Latin and Brazilian rhythm, which he pursues on his own terms across Sambao, Canta Brasil and Kenny Barron & the Brazilian Knights, and eleven years in Sphere made him one of the most idiomatic non-alumni interpreters of Monk. The Los Angeles Times has called him "one of the top jazz pianists in the world," and Jazz Weekly the "most lyrical piano player of our time." Through twenty-six years at Rutgers and his current post at Juilliard he has taught Aaron Parks, Peter Bernstein, David Sanchez, Harry Pickens, Jon Regen and Earl MacDonald, among a long list of working professionals.