Ensign was born in Safford, Arizona and was raised in both the United States and England. He trained at the London Academy of Music and Dramatic Art and spent the first ten years of his professional career working in the theatre in Britain.
He was a member of the Royal Shakespeare Company and appeared in Irene, Curse of the Starving Class, and The Red Devil Battery Sign in the West End.
Ensign also voices Dr. Nefarious Tropy in most of the Crash Bandicoot games with the exception of Crash Bandicoot: The Wrath of Cortex, in which Corey Burton voiced the character.