Sullivan was born and raised in the San Francisco, Bay Area. In college, he played basketball and majored in Theater at Brown University, before transferring to the UCLA School of Theater, Film, and Television. Sullivan's breakout came in the 2019 Off-Broadway production of "Slave Play" at New York Theater Workshop. Directed by Robert O'Hara and written by Jeremy O. Harris, "Slave Play" eventually transferred to Broadway and was nominated for 13 Tony awards. Since then, Sullivan has appeared in TV series for Netflix, Hulu, HBO, FX, Amazon and in feature films for A24 and Sony.