John Robert Smith was born on December 16, 1933, in Louisville, Kentucky. He started on piano as a child, admired Bud Powell and Art Tatum, and worked as a pianist before he took up the organ, playing with the saxophonist Paul Williams and the drummer Chris Columbo. After moving to Cleveland he heard the organist Wild Bill Davis and decided to switch to the Hammond B-3, and he made his professional debut on the organ in 1958, around the time he was accompanying the singer Nancy Wilson. His first record as a leader, a 1958 organ trio album called Have You Heard for the Arrow label, has Columbo on drums and was credited to Johnny Smith.

The "Hammond" in his billing was a nickname taken from his instrument, and it solved a practical problem: there was already a well-known guitarist named Johnny Smith, and the most famous organist in jazz was Jimmy Smith. By the time he began recording for Prestige's New Jazz subsidiary in 1959 he was Johnny "Hammond" Smith. All Soul, recorded on September 11, 1959, at Rudy Van Gelder's studio in Englewood Cliffs, New Jersey, and That Good Feelin' paired him with the guitarist Thornel Schwartz, the bassist George Tucker and the drummer Leo Stevens. His working bands over the next decade featured the saxophonists Houston Person and Earl Edwards, the guitarists Eddie McFadden, Floyd Smith and James Clark, the vibraphonist Freddie McCoy, and the singers Etta Jones and Byrdie Green.

The 1960s were his Prestige decade, with a stretch at Riverside in between. For Prestige he made Talk That Talk (1961), with Oliver Nelson on tenor saxophone for three tracks and Ray Barretto on congas; Gettin' the Message, recorded on October 14, 1960, with the vibraphonist Lem Winchester; and Johnny "Hammond" Cooks with Gator Tail, recorded on June 6, 1962, with the tenor saxophonist Willis Jackson. At Riverside he recorded Black Coffee live at the Monterey Club in New Haven, Connecticut, on November 8, 1962, with the tenor saxophonist Seldon Powell, followed by Mr. Wonderful (1963) with Houston Person and the trumpeter Sonny Williams, Open House! with Thad Jones, Powell, Barretto and the bassist Bob Cranshaw, and A Little Taste. Back at Prestige from 1965 he made The Stinger (recorded May 7, 1965), the vocal date The Stinger Meets the Golden Thrush with Byrdie Green, and a run of funkier records: Soul Flowers, Dirty Grape, Nasty! (1968, with Person, the guitarist John Abercrombie and the drummer Grady Tate), Soul Talk and Black Feeling! (1969, with the drummer Bernard Purdie) and Here It 'Tis (1970). AllMusic dates the Prestige association from 1959 to 1970.

In 1971 he moved to the CTI family of labels run by the producer Creed Taylor and shortened his billing to Johnny Hammond. Breakout, recorded on June 3 and 4, 1971, at Van Gelder's studio, was the first release on CTI's new Kudu imprint. Its band included Grover Washington Jr., then a sideman a few years before his own breakthrough, along with the altoist Hank Crawford, the guitarist Eric Gale, the drummer Billy Cobham and the percussionist Airto Moreira. Wild Horses Rock Steady (recorded in the autumn of 1971, with arrangements by Bob James) followed, then The Prophet, recorded on November 29 and 30, 1972, with horn arrangements by Pee Wee Ellis and a solo from Maceo Parker, and Higher Ground, recorded on October 31 and November 1, 1973, with Bob James again arranging and a band that included Joe Henderson, George Benson, Ron Carter and Steve Gadd. He also played the CTI all-star concert at the Hollywood Palladium on July 18, 1971, issued as California Concert.

His biggest change of sound came on the West Coast. For Gambler's Life (1974), recorded in June 1974 at the Sound Factory in Hollywood and issued on CTI's Salvation label, he worked with the producers Larry Mizell and Fonce Mizell and added electric piano and synthesizer to his organ. The same team made Gears (1975) for Milestone, recorded at Fantasy Studios in Berkeley in July 1975. Three more Milestone albums followed: Forever Taurus (1976), produced and arranged by Wade Marcus; Storm Warning (1977), which he produced and arranged himself; and Don't Let the System Get You (1978), on which he also sang. AllMusic says he then largely stepped back from jazz, settled in Southern California and invested in real estate. From January 1987 he taught in the music department at Cal Poly Pomona, and he wrote "Quiet Fire" for Nancy Wilson's album Nancy Now! (1988). He passed away of cancer on June 4, 1997, in Victorville, California, at the age of 63.

Smith belongs to the soul-jazz and hard bop organ tradition, and AllMusic calls him one of its more underrated players. His roots were pianistic: he came to the organ from piano, and one biography ties his phrasing to Erroll Garner. His early records are made of blues, ballads and medium-tempo grooves in a trio or quartet with guitar, and the Prestige albums grew steadily funkier, with Latin percussion and a Fender bass underneath. At Kudu and Milestone he turned to electric piano and synthesizer, to long vamps and to the Mizell brothers' layered, rhythm-section-driven sound. AllMusic observes that jazz purists disliked Gears while acid jazz fans embraced it, and his Kudu and Milestone records have since been sampled and reissued widely: "Shifting Gears" appears on the breakbeat compilation Ultimate Breaks and Beats, and the group BadBadNotGood has recorded its own version of "Los Conquistadores Chocolates." His own influences include Bud Powell and Art Tatum on piano and Wild Bill Davis on organ.