Keyon Karim Harrold was born on November 18, 1980, in Ferguson, Missouri, one of 16 children in a family of musicians. His grandfather, a former police officer, founded the Memorial Lancers Drum and Bugle Corps, and Harrold played in it from about age six to seventeen. He met the pianist Robert Glasper at a summer jazz camp run by the Vail Jazz Foundation in Colorado, moved to New York City with his childhood friend, the drummer Mark Colenburg, and graduated from the School of Jazz at The New School, where Glasper was a classmate.

His first professional job came through Glasper: on his recommendation Harrold auditioned for the rapper Common, won the trumpet chair on Common's tour, and then recommended Colenburg for the band as well. He also became a mentee of the trumpeter Charles Tolliver and played in Tolliver's big band on With Love (2006, Blue Note), where he is credited on three of the seven tracks, and on the live Emperor March: Live at the Blue Note (2009). By then he was working across New York's jazz clubs and the city's studios at once. Discogs credits him on records by Mobb Deep (2006), John Legend (2006), Beyoncé (the 2006 album B'Day), Jay-Z (American Gangster, 2007), 50 Cent (Curtis, 2007) and Maxwell (BLACKsummers'night, 2009), alongside jazz sideman dates for Billy Harper (Blueprints of Jazz, Vol. 2, 2008), David Sanborn (Here & Gone, 2008) and the bassist Derrick Hodge (Live Today, 2013).

His debut as a leader, Introducing Keyon Harrold, was recorded on June 14, 2008, at Systems Two in Brooklyn and issued by the Criss Cross label in September 2009. It is a quintet date with the saxophonist Marcus Strickland, pianist Danny Grissett, bassist Dezron Douglas and drummer E.J. Strickland, and Harrold wrote most of its material. Charles Tolliver joins on the opener, and Harrold's brother Emanuel, a drummer, plays on "Keyon Beyond." AllMusic called the album a promising start and named him one of the leading trumpeters of a new generation. In the years that followed he recorded on Gregory Porter's Be Good (2012) and Take Me to the Alley (2016), on Strickland's Nihil Novi (2016) and on Dr. Lonnie Smith's Evolution (2016), and toured with Common, D'Angelo, Maxwell, Mary J. Blige and Gregory Porter, among others.

The wider public heard him first in the film Miles Ahead (2015), in which Don Cheadle plays Miles Davis. Glasper, who composed the film's new music, brought Harrold in to supply every note of trumpet in several eras of Davis's sound; on set he played the parts while Cheadle matched his fingering. Harrold is credited on at least four tracks of the soundtrack album, released April 1, 2016, which won the Grammy Award for Best Compilation Soundtrack for Visual Media at the 59th Grammy Awards.

The Mugician, released on September 29, 2017, by Legacy and Mass Appeal, is his second album as a leader. Harrold produced it, is credited with the music on all twelve tracks, sings on four and also plays piano and flugelhorn. Drummers Chris Dave and Mark Colenburg, guitarist Nir Felder, keyboardists Shedrick Mitchell and James Poyser, bassist Pino Palladino on one track, and Strickland on saxophone and bass clarinet make up the band, and Big K.R.I.T. and Georgia Anne Muldrow are among the lyric writers. His mother, Shirley Harrold, is credited with the words to the opening track, "Voicemail," with relatives singing backing vocals.

On December 26, 2020, in the lobby of the Arlo SoHo hotel in Manhattan, a woman falsely accused Harrold's 14-year-old son of stealing her phone and grabbed him while Harrold filmed. The video drew wide attention, the phone turned up in a car she had ridden in, and she was arrested in January 2021 and later accepted a plea deal. In 2021 Jazz St. Louis named him its first creative adviser, a three-year appointment funded by the Mellon Foundation that included a commissioned work for the end of its 2023-2024 season. As of January 2024 he was living in Los Angeles.

Foreverland (Concord Jazz, January 19, 2024) is his third album as a leader. It grew from an informal studio session with friends in Las Vegas on his birthday during the early pandemic, and he sings more on it than on earlier records, with Common, Glasper and Jean Baylor on "Find Your Peace," PJ Morton on "Beautiful Day," and Laura Mvula on the title track. It was nominated for Best Alternative Jazz Album at the 67th Grammy Awards. In February 2023 he played eight shows at New York's Blue Note with the Karl Denson Project, and in June 2025 he recorded Live at Vic's Las Vegas, the Nicole Zuraitis album that also features drummer Dan Pugach and Tom Scott, which brought two more Grammy nominations at the 68th ceremony, for Best Jazz Performance and Best Jazz Vocal Album. The Recording Academy lists him with three nominations and no wins as of November 5, 2026. His most recent record is Straight08, released June 19, 2026, by La Reserve, a chordless trio with keyboardist Sam Barsh and drummer Mark Guiliana, recorded in a single session on August 22, 2023, in Long Beach, California.

Harrold names Miles Davis's second great quintet, Prince, Common, Dr. Dre and J Dilla as influences, and his music sits where those meet: bop-rooted trumpet over hip-hop drums and neo-soul harmony, with a singing voice of his own on recent records. Discogs credits show him in the Harmon mute and on flugelhorn on Hodge's Live Today and in muted trumpet on Robert Glasper's Black Radio III (2022), and he has been a regular in Glasper's circle since their New School years. His first album is straight post-bop, The Mugician and Foreverland fold in R&B, gospel and rap, and Straight08 returns to open improvisation. Much of his studio work for pop, R&B and hip-hop artists is outside jazz, which is why only the jazz-adjacent tags above are used for him.