O'Neal was born in Detroit to a pianist father and grew up playing gospel piano at church and boogie-woogie at night. Intrigued by the jazz sound of legends Oscar Peterson, Art Tatum and Bud Powell, he taught himself by listening to the greats began pursuing a career in jazz. He moved to Birmingham in 1974 and established himself as a working musician, never needing a day job to make ends meet.
O'Neal moved to New York City to perform with Clark Terry in 1981. He also landed a regular job at the Blue Note, eventually accompanying such greats as Dizzy Gillespie, Ray Brown, Nancy Wilson, Joe Pass and Kenny Burrell.
Oscar Peterson recommended O'Neal for the role of Art Tatum in the 2004 biographical film Ray. Tatum and star Jamie Foxx recreated a scene where Ray Charles listened in awe to Tatum playing before a Toledo audience. His live performance of Tatum's signature "Yesterdays" convincingly recreated the master's sound and has brought wide acclaim to O'Neal.
- O'Neal, Johnny (1983) Coming Out. Concord Jazz.
- O'Neal, Johnny (1985) Soulful Swinging. Parkwood.
- O'Neal, Johnny (1985) Live at Baker's Keyboard Lounge. Parkwood.
- O'Neal, Johnny (1995) On the Montreal Scene. Justin Time
- Stan Getz Quartet (2002) Pure Getz.
- O'Neal, Johnny (2002) In Good Hands. Jazzabel