He began his career on stage in the West End before having a screen career, which included starring in a 1954 BBC adaptation of George Orwell's Nineteen Eighty-Four, before playing numerous supporting and character roles in films including RAF Flight Lieutenant Colin Blythe in The Great Escape (1963), the villain Ernst Stavro Blofeld in the James Bond film You Only Live Twice (1967), SEN 5241 in THX 1138 (1971), and the deranged Clarence "Doc" Tydon in Wake in Fright (1971).

The series' popularity and critical success led to a resurgent career for Pleasence, who appeared in numerous American and European-produced horror and thriller films.

For eighteen months he worked as a booking clerk at Swinton railway station,[23] with LNER[24] and decided that he wanted to be a professional actor, taking up a placement with the Jersey Repertory Company in 1939.

On 31 August 1944, his Lancaster NE112 was shot down during an attack on Agenville, France,[27][28] and he was captured and imprisoned in the German prisoner-of-war camp Stalag Luft I. Pleasence produced and acted in many plays for the entertainment of his fellow captives.

[31] In the 1950s, Pleasence's stage work included performing as Willie Mossop in a 1952 production of Hobson's Choice at the Arts Theatre, London and as Dauphin in Jean Anouilh's The Lark (1956).

[30] In 1960, Pleasence gained excellent notices as the tramp in Harold Pinter's The Caretaker at the Arts Theatre, a role he would again play in a 1990 revival.

[30] Pleasence's later stage work included performing in a double bill of Pinter plays, The Basement and Tea Party, at the Duchess Theatre in 1970.

Noting his involvement in the original film, Joan Hanauer wrote that Pleasence had "graduated to an S.S. villain, and he is a marvel of soft-spoken, almost finicky evil.

[36] Endowed with a bald head, a penetrating stare, and an intense voice, usually quiet but capable of a piercing scream, he specialised in portraying insane, fanatical, or evil characters, including the title role in Dr Crippen (1962), the frontier prophet Oracle Jones in Hallelujah Trail, the double agent Dr Michaels in the science-fiction film Fantastic Voyage (1966), the white trader who sells guns to the Cheyenne Indians in the revisionist western Soldier Blue (1970), the mad German psychoanalyst with Bud Spencer–Terence Hill in Watch Out, We're Mad!

In the crime drama Hell is a City (1960), shot in Manchester, he starred opposite Stanley Baker, while he was memorably cast in the horror comedy What a Carve Up!

He appeared as the mild-mannered and good-natured POW forger Colin Blythe in the film The Great Escape (1963), who discovers that he is slowly going blind, but nonetheless participates in the mass break-out, only to be shot down by German soldiers because he is unable to see them.

In 1971, he returned to the realm of the deranged, delivering a tour de force performance in the role of an alcoholic Australian doctor in Ted Kotcheff's nightmarish outback drama Wake in Fright.

He ventured successfully into American cowboy territory, playing a sadistic self-styled preacher who goes after stoic Charlton Heston in the Western Will Penny (1968).

The next year he appeared as an eccentric, tea-obsessed police inspector in the cult horror film Death Line alongside Norman Rossington and Christopher Lee.

A few years later, he portrayed antagonist Lucas Deranian, in Walt Disney's Escape to Witch Mountain (1975) and, in Telefon (1977), Nicolai Dalchimsky, the Russian seeking to start a war between the United States and the Soviet Union.

He also played the teacher, Kantorek in All Quiet on the Western Front (1979), Dr. Kobras in The Pumaman (1980) and the held-hostage President of the United States in Escape from New York (1981).

"[43] The reviewer from Horror Society wrote of liking Schanley and Pleasence "but the story is the main focus here and not the cast which is a bit of a shame because both did fantastic jobs.

"[44] Operation Nam was Pleasence's sole film appearance in 1986, playing "a minor part as a priest" who services Vietnam soldiers.

[45] Pleasence collaborated with Carpenter again when he starred in Prince of Darkness (1987), where he played a priest who seeks the aid of a professor and a few of the latter's quantum physics students to uncover the mystery of a glowing liquid in a canister.

Two years earlier, Pleasence did an amusingly broad impersonation of Olivier in the guise of a horror-film actor called "Valentine De'ath" in the film The Uncanny (1977).

According to the film critic Kim Newman on a DVD commentary for Halloween II, the reason for Pleasence's lengthy filmography was that he never turned down any role that was offered.

[51] Pleasence was the author of the children's book Scouse the Mouse (1977) (London: New English Library), which was animated by Canadian animator/film director Gerald Potterton (a friend of the actor, who directed him in the Canadian film The Rainbow Boys (1973), retitled The Rainbow Gang for VHS release in the United States) and also adapted into a children's recording (Polydor Records, 1977) with Ringo Starr voicing the book's title character, Scouse the Mouse.

In his book British Film Character Actors (1982), Terence Pettigrew describes Pleasence as "a potent combination of eyes and voice.

Pleasence was nominated four times for the Tony Award for best performance by a leading actor in a Broadway play: in 1962 for Harold Pinter's The Caretaker, in 1965 for Jean Anouilh's Poor Bitos, in 1969 for Robert Shaw's The Man in the Glass Booth, and in 1972 for Simon Gray's Wise Child.

Pleasence was appointed an Officer of the Most Excellent Order of the British Empire for his services to the acting profession by Queen Elizabeth II in 1994.

Evil, the character played by Mike Myers in the Austin Powers comedy films (1997–2002), and Doctor Claw from Inspector Gadget are parodies of Pleasence's performance as Blofeld in You Only Live Twice.