[1] A graduate of the Royal Academy of Dramatic Art, he was a star of British B-movies in the 1950s and 1960s, but gained widespread recognition for his role as Dr. Heywood Floyd in the landmark science-fiction film 2001: A Space Odyssey (1968).

[2] As a result, he gained top billing in one of his first films, House of Blackmail (1953), directed by the veteran filmmaker Maurice Elvey, for whom he also made What Every Woman Wants the following year.

He also starred in such minor films as A Stranger Came Home (1954, for Hammer), Dublin Nightmare (1958), Offbeat (1961), Information Received (1961), Incident at Midnight (1963), Blind Corner (1964), and Ring of Spies (1964).

Sylvester was cast by director Stanley Kubrick as Dr. Heywood R. Floyd in the landmark film 2001 A Space Odyssey (1968).

Sylvester retired from acting during the early 1980s, and died of undisclosed causes in Sacramento, California, on January 25, 1995, six days before his 73rd birthday.