[1] He was best known for his close association with cult filmmaker Jesús Franco, appearing in 40 of the director’s films, beginning with the titular character in The Awful Dr. Orloff (1962).

[1][2] A prolific character actor, Vernon also worked with many other prominent filmmakers, notably Jean-Luc Godard, Jean-Pierre Melville, René Clément, Powell & Pressburger, Sacha Guitry, Fritz Lang, John Frankenheimer, Roger Vadim, Fred Zinnemann, Woody Allen and Jean-Pierre Jeunet.

[3] At the outbreak of World War II and the occupation of France, Vernon was employed by Fernsehsender Paris, the German-run television broadcaster, as he was bilingual and from a neutral country.

Horror film fans consider his three greatest horror roles to be The Awful Dr. Orloff (1962) which introduced Franco's famed mad doctor character, Dracula vs. Frankenstein (1971) in which he actually played Count Dracula, and The Erotic Rites of Frankenstein (1972) in which he played Count Cagliostro.

Between his work with Franco, whom he came to consider a personal friend, he continued to appear in more high-profile projects, and was active as a dubber.