The son of a minister, Mitchell began working on Broadway and participated in an experimental television broadcast. When World War II was declared, Mitchell enlisted in the US Army Air Force and served as a bombardier.
In 1945 Mitchell made his film debut in the film What Next, Corporal Hargrove? He played the role of Happy in both the stage and screen versions of Death of a Salesman. Later in his career, he worked extensively in television.
- Stranded in Space (Experiment #305) - as George Benedict
- Space Mutiny (Experiment #820 and RiffTrax) - as Alex Jansen
- Frankenstein Island (Rifftrax) - as Clay Jayson
- Viva Knievel! (Rifftrax) - as Barton
- Supersonic Man (Rifftrax) - as Dr. Gulik
- Flight to Mars (Rifftrax Presents) - as Steve Abbott
- Deadly Prey (Rifftrax) - as Jaimy's Father
- Jack-O (RiffTrax) - as Dr. Cadaver