Early in his career, Mabern played in Chicago with MJT + 3 in the late 1950s and then moved to New York in 1959. Mabern has worked with Jimmy Forrest, Lionel Hampton, the Jazztet (1961-1962), Donald Byrd, Miles Davis (1963), J.J. Johnson (1963-1965), Lee Morgan (1965), Sonny Rollins, Freddie Hubbard, Wes Montgomery, Joe Williams (1966- 1967), and Sarah Vaughan.
In the late 1960s and early 1970s, Mabern led four albums for Prestige Records, performed with Lee Morgan, and recorded with Stanley Cowell's Piano Choir. Harold Mabern has recorded as a leader for DIW/Columbia and Sackville and toured with the Contemporary Piano Ensemble (1993-1995).
A longtime faculty member at William Paterson College, Mabern is a frequent instructor at Stanford Jazz Workshop.
Saxophonist Eric Alexander was one of Mabern's students at William Pattereson in the late 1980s. Mabern now frequently tours and records with Alexander as part of his quintet. To date, Mabern and Alexander have appeared on over twenty CDs together.