He is married with one daughter and two sons and resides in California.
O'Bannon grew up the son of a gaffer, surrounded by film from his birth. His father worked on various films through Warner Bros. golden age, and his mother was a professional dancer who performed with Fred Astaire.
He started writing in high school, and wrote many spec scripts (works written "on speculation", without a verbal or written contract), and eventually submitted them to NBC's Amazing Stories and CBS's The Twilight Zone (1985). CBS bought one of them, and after a second script sale for The Twilight Zone, he was hired on as a staff writer.