Poussaint was born in New York City' [[East Harlem]from Haitian immigrants neighborhood, and graduated from Stuyvesant High School in 1952. As a youth, he took ill with rheumatic fever, which left him unable to engage in the physical activities of his peers. The academic pursuits that characterized his early years led him to graduate from Columbia University in 1956, acquire a M.D from Cornell University in 1960, and complete postgraduate training from the University of California, Los Angeles, where he studied psychopharmacology and served as Chief Resident in Psychiatry.

After his initial academic accomplishments, Poussaint took part in the civil rights movement, which solidified his notion that racism resides at the core of mental health problems in the black community. Later in life, Poussaint served as a consultant for The Cosby Show and currently combines an advocacy for responsible media programming with his academic work.

Along with Bill Cosby he co-authored the 2007 book Come On People: On the Path from Victims to Victors.