The son of Thoroughbred horse trainer Harold Theriot, he is a nephew of jockey Larry Melancon.
Theriot, who began riding on bush tracks in his native Louisiana, turned professional at age 16.
On May 17, 2008, he rode in his first American Classic, taking sixth place aboard Kentucky Bear in the Preakness Stakes at Pimlico Race Course.
That June 18, he became the seventh rider in Churchill Downs history to ride six winners in a single day.
Born To Be clipped the horse running in front of her, knocking her unconscious and throwing Douglas headfirst into the track, paralyzing her from the waist down.