Tim Thomerson was born in Coronado, California. He was brought up in Hawaii and in San Diego. Following a stint in the National Guard where he was with actor Brion James, Thomerson chose to become an actor, while taking a job as a set builder and prop man at the Old Globe Theatre, which is famous for its Shakespearean productions. After meeting character actor Anthony Zerbe, he took Anthony's advice and studied acting, at the Herpolscheimer School of Performing Arts, with Stella Adler in New York City.
After his college tenure had ended, Thomerson began a career as a stand-up comedian, honing his skills. He appeared in clubs that included The Bitter End in Greenwich Village, The Improv in Los Angeles, Catch a Rising Star, and the Catskills.
Thomerson's wife Teri Blythe has worked extensively in Hollywood as a script supervisor, make-up artist, casting director, and producer.