She was married to professor-turned-actor Dennis Letts until his death in 2008, and is the mother of playwright/actor Tracy Letts, jazz musician/composer Shawn Letts, and Dana Letts.
Letts was born as Billie Gipson in Tulsa, Oklahoma. She married Dennis Letts, a professor and actor, in 1958. He served as his wife's editor for her own novels. Dennis Letts died of cancer in Tulsa on February 22, 2008, aged 73.
Billie Letts is a member of the Sigma Sigma Sigma sorority.