Weldon was born in Hampton, Virginia, on October 27, 1943 to Weldon Irvine Sr. and Virginia Brown Irvine. Raised by his grandparents Major and Mrs. Walter R. Brown on the campus of Hampton Institute in the house known as "The Lodge". While his grandmother played standup bass in a series of regional classical ensembles, her husband served as dean of the men's college at Hampton Institute. While attending Phenix High School, young Weldon developed a penchant for writing. He graduated from George P. Phenix High School in 1961. Irvine began playing piano as a teen, and while he later majored in literature at Hampton, music remained his first love, especially after discovering jazz. Keyboardist Weldon Irvine looms large in the pantheon of jazz-funk, profoundly influencing the subsequent generations of hip-hop artists for whom he served as collaborator and mentor. Upon settling in New York City in 1965, he signed on with Nina Simone as the legendary singer's organist, bandleader, arranger, and road manager. After seeing a performance of playwright Lorraine Hansberry's To Be Young, Gifted and Black, Simone instructed Irvine to compose lyrics for a song of the same title. The finished song would later merit cover versions by performers including Aretha Franklin, Stevie Wonder, and Donny Hathaway on its way to becoming the best known of his approximately 500 published compositions. "To Be Young, Gifted, and Black", performed live for the first time by Simone on the album Black Gold (1970). It has been dubbed the "official" Civil Rights anthem.
After splitting from Simone, Irvine formed his own 17-piece group that at different times included the likes of Billy Cobham, Randy Brecker, Bennie Maupin, and Don Blackman.
April 9, 2002 Weldon Irvine, Jr. said farewell to the world, leaving behind a son Weldon Irvine III.