Vernon was born Mario Lippert in Baden, Switzerland, to a Swiss father and an American mother, and was fluent in German, English and French. Originally a stage and radio actor, he worked primarily in France and became a well-known supporting actor after 1945 by playing villainous Nazi officers in French films. Jean-Pierre Melville's Le Silence de la mer, in which he played a gentle anti-Nazi German officer, made him somewhat famous, but, in part due to his looks and Swiss accent, he was subsequently relegated to playing Gangsters and heavies.

In the 1960s, he became a favorite actor of Spanish horror Director Jesús Franco and began starring in many low-budget horror movies produced in Spain or in France, often portraying a mad Doctor named "Dr. Orloff". He continued to make increasingly small appearances in high-profile films while often getting top billing in many Grade-Z horror films. Horror fans consider his three greatest horror film roles to be The Awful Dr. Orloff (1961) which introduced Franco's famed mad Doctor character, Dracula vs Frankenstein (1971) in which he played Count Dracula and The Erotic Rites of Frankenstein (1972) in which he played the insanely evil Count Cagliostro.

He remained active until his death from natural causes in 1996. He died in Paris, France, 10 days after his 82nd birthday.