Billy Bob Thornton was born on August 4, 1955, in Hot Springs, Arkansas, the son of Virginia Roberta (née Faulkner; died July 29, 2017), a self-proclaimed psychic, and William Raymond "Billy Ray" Thornton (November 1929 – August 1974), a high school history teacher and basketball coach. His brother, Jimmy Don (April 1958 – October 1988), wrote a number of songs, two of which ("Island Avenue" and "Emily") Thornton has recorded on his solo albums. He is of part Irish descent. He also has another brother John David Thornton.
In the mid-1980s, Thornton settled in Los Angeles, California, to pursue his career as an actor, with future writing partner Tom Epperson. He had a difficult time succeeding as an actor and worked in telemarketing, offshore wind farming, and fast food management between auditioning for acting jobs. He also played the drums and sang with South African rock band Jack Hammer. While working as a waiter for an industry event, he served film director and screenwriter Billy Wilder. He struck up a conversation with Wilder, who advised Thornton to consider a career as a screenwriter.