Peter Wyngarde's date and place of birth, his birth name, and his parents' nationalities and occupations are all disputed. According to his own account, he was born Peter Paul Wyngarde on 23 August 1933 to a French mother and a British father named Wyngarde at an aunt's home in Marseille, France. He claimed that his father worked for the British Diplomatic Service in Hong Kong, Malaya, Singapore and India, before becoming an importer-exporter living in Eaton Square, London. He also claimed to be the nephew of French actor and Director Louis Jouvet.

Other evidence suggests that Wyngarde's original name was Cyril Louis Goldbert and that he changed his name after arriving in the UK in the mid-1940s. Author J. G. Ballard, with whom he endured the Japanese internment camp Lunghua, said that he and his family knew Wyngarde as Cyril Goldbert in Shanghai during the Second World War, but in interviews Wyngarde denied knowing Ballard. Peter Wyngarde's mother was Marcheritta "Madge" Goldbert, née Ahin, later Macauley. The Ahins were a Eurasian family living in Singapore in the 1890s. Records indicate that she was a Swiss national and that she re-married in 1947 and moved to Malaysia.

In Wyngarde's own accounts of his life he said that he was living in Shanghai when the Japanese Army took over the Shanghai International Settlement on 8 December 1941, and began acting during his internment when he played all the characters in a version of Doctor Jekyll and Mr Hyde. In April 1943 Cyril Goldbert was interned in the Lunghua civilian internment camp.

Correspondence held in the UK's National Archives shows that in 1942/43 the 15-year-old son of merchant seaman Henry Goldbert, and his two younger siblings, were living in Shanghai. Efforts were made by the UK's Ministry of War Transport, the Prisoners of War Department and various boarding schools to facilitate the children's repatriation from Shanghai to the UK, but the older boy could not be accommodated because of his age.

Following liberation, Cyril Goldbert sailed from Shanghai to Southampton on the Cunard White Star line ship Arawa. He is listed as an 18-year-old Passenger travelling alone, and his next of kin in the UK is named as Mr H. Goldbert. After arrival in the UK on 14 December 1945, Cyril Goldbert is not found in any further UK public records.

In 1946, Wyngarde took his first professional roles in theatre productions, first appearing at the Buxton Playhouse, and the following year in a production of Noël Coward's Present Laughter at the Theatre Royal, Birmingham. He appeared with Alec Guinness in Hamlet in London in 1951 and with Siobhán McKenna in Saint Joan in 1954. His theatre appearances included playing opposite Vivien Leigh in 1958, and as Cyrano de Bergerac at the Bristol Old Vic in 1959, which he considered a highlight of his career.

Wyngarde said he had been married to the Actress Dorinda Stevens for several years in the 1950s, and a Dorinda and Peter Wyngarde are shown living together on the 1953 electoral roll for Holland Park. From 1956 to 1958 he was living with Ruby Talbot in London. In the 1960s, he shared a flat with fellow actor Alan Bates; according to some sources this was a sexual relationship. It was well known within the acting community that Wyngarde was gay – reputedly he acquired the nickname Petunia Winegum, though this was disputed by others who said that the name had merely been invented for a comedy Sketch.

Wyngarde's film work was not extensive, but gained attention. He took the role of Pausanias opposite Richard Burton in the film Alexander the Great (1956), and appeared in the film The Siege of Sidney Street (1960). In Jack Clayton's The Innocents (1961), he had brief unspeaking scenes as the leering Peter Quint with Deborah Kerr and Pamela Franklin. He followed this appearance as the lead in the occult thriller Night of the Eagle (US title: Burn Witch Burn, 1962), his only film appearance in a lead role.

By the late 1960s, Wyngarde was guest starring in television series of the time, many of which were shown internationally, including The Avengers, The Saint, The Baron, The Champions and I Spy. He also appeared in The Prisoner ("Checkmate", 1967) as the authority figure called Number Two. Wyngarde was also a guest star, playing himself as a Shakespearean actor in the 1966 prime-time TV special, Lucy in London starring Lucille Ball.

Wyngarde became a British household name through his starring role in the espionage series Department S (1969). His Jason King character, a Novelist turned sleuth, was reputedly based on the author Ian Fleming. King led a hedonistic lifestyle; he often got the girl but as she is about to kiss him manages to avoid it, much to the annoyance of co-actor Joel Fabiani. After that series ended, his character, the suave womaniser Jason King, was spun off into a new action espionage series entitled Jason King (1971), which ran for one season of 26 fifty-minute episodes.

In 1970, Wyngarde recorded an album released by RCA Victor entitled simply Peter Wyngarde, featuring a single, "La Ronde De L'Amour"/"The Way I Cry Over You". The album is a collection of spoken-word musical arrangements produced by Vic Smith and Hubert Thomas Valverde. Wyngarde claimed that: "It sold out in next to no time... but RCA point-blankly refused to press any more. I was fuming, as I’d been given a three-album contract with the company, who promised to release one LP every 12 months. The excuse was that production was being moved... They told me that everything would have to go on the back burner, but I just believe that they got cold feet". A promo single of the track "Rape" (entitled "Peter Wyngarde Commits Rape") was also issued in 1970.

A revival in October 1973 of The King and I, featuring Wyngarde in the male lead role, and initially with Sally Ann Howes as Anna, ran for 260 performances at the Adelphi Theatre in London. In the late 1970s he performed in the theatre in South Africa and Austria. Also on stage he appeared in the thriller Underground with Raymond Burr at the Royal Alexandra Theatre, Toronto, and at the Prince of Wales Theatre, London in 1983.

Public attention was drawn to his behaviour in September 1975 when he was fined £75 (under his probable real name, Cyril Louis Goldbert) for gross indecency with a crane driver in public toilets in Gloucester bus station. This followed an arrest and caution for similar acts in the toilets at Kennedy Gardens in Birmingham the previous year.

Wyngarde played the masked character Klytus in the film Flash Gordon (1980) and Sir Robert Knight in the film Tank Malling (1989) with Ray Winstone. On TV he appeared in The Two Ronnies 1984 Christmas Special as Sir Guy. Other TV appearances include Doctor Who (in the four-episode-story Planet of Fire, 1984), Hammer House of Mystery and Suspense (1984), Bulman (1985), The Lenny Henry Show (1994) and The Memoirs of Sherlock Holmes (1994).

A Peter Wyngarde appreciation society, The Hellfire Club, was founded in 1992 with Wyngarde's support, with members receiving its quarterly magazine by post. It went online in 2000, and maintains a regularly updated blog and Facebook page.

Wyngarde was an alcoholic at the height of his career, telling an interviewer in 1993 "I drank myself to a standstill ... I am amazed I am still here", but that he stopped drinking in the early 1980s. After regular acting work dried up in the 1980s, he was declared bankrupt and was reported as living on social security benefits.

After leaving a 1995 stage production of The Cabinet of Dr Caligari due to a throat infection while still in previews Wyngarde mostly stopped acting but did occasional voice work.

In 1998, the album was reissued on CD by RPM Records, re-titled When Sex Leers Its Inquisitive Head. The album is now usually treated as a curiosity because of its unusual spoken-word style and the controversial subject matter of some of the tracks.

He appeared as a guest of Simon Dee in the Channel Four one-off revival of his chat show Dee Time in 2003. In 2007, he participated in recording extras for a box-set of The Prisoner, including a mock interview segment titled "The Pink Prisoner".

In January 2014, he narrated an episode of the BBC 4 Timeshift documentary strand, How to Be Sherlock Holmes: The Many Faces of a Master Detective. In the 2015 documentary series for Channel Four, It was Alright in the 1960s, Wyngarde expressed his unease at having to don blackface to play a Turk in The Saint, but said that he had done it only in the hope that a theatre Director might pick him to play Othello.

His agent and manager reported that Wyngarde was admitted to the Chelsea and Westminster Hospital in London in October 2017 with an unspecified illness. He died on 15 January 2018.