Born in Harlem and raised in Queens, Onaje started playing piano at age 7. He attended Manhattan’s Music and Art High School and was mentored by Leroy Kirkland of Erskine Hawkins’ band. He was already playing professionally and developing an interest in R&B and straight-ahead jazz. He went on to study music at the State University of New York at Fredonia.
In 1971, a gig with Kenny Burrell at Baker's Keyboard Lounge in Detroit led to work with Major Holley and the Thad Jones-Mel Lewis Orchestra. By 1973, he was recording and doing sideman gigs with musicians like Buster Williams, Cecil McBee, Betty Carter and Nat Adderley. A two-year pianist/arranger stint with Woody Shaw's band followed as did composing for the albums Moontrane and Rosewood, for which he garnered a Down Beat Reader’s Poll Award for Best Jazz Group and Best Jazz Album. Onaje works as a sideman and arranger to this day, most notably with vocalist Cassandra Wilson.
Other projects include Onaje (Steeplechase), That Special Part of Me (1988), and Dare to Dream (1991). The former included his most enduring composition, Quiet Passion, now on smooth jazz rotations for two decades. Recent releases include Return to Form (Half Note), Remember Their Innocence (Ejano), and Sack Full of Dreams (2007,18th & Vine) which was a Jazz Improv Magazine pick best albums of 2007 pick. Onaje composed, arranged and performed the original score for the Showtime film, Override, directed and produced by Danny Glover. He is a 2006 NAACP Image Award Nominee for Outstanding Jazz Artist. Onaje has been a resident artist at the Litchfield Jazz Camp since 2009.