Sellers was born in Southsea, England to a family of entertainers. His parents nicknamed him Peter at an early age, after his elder stillborn brother. He attended a Roman Catholic school, St. Aloysius College, although his father was Protestant and his mother was Jewish. He was a descendant of English prizefighter Daniel Mendoza, who was of Portuguese-Jewish descent. Sellers was also a cousin of Talksport radio presenter Mike Mendoza.

Accompanying his family on the variety show circuit, Sellers learned stagecraft which proved valuable later. He performed at five at the Windmill Theatre in the drama Splash Me!, which featured his mother. He was a versatile artist, excelling at dancing, drumming well enough to tour with jazz bands (his drumming is shown in a clip of The Steve Allen Show in 1964), and playing ukulele and banjo. In Parkinson, Sellers claimed his father had taught George Formby to play ukulele. Sellers played ukulele on the "New York Girls" track for Steeleye Span's 1975 album Commoner's Crown.

During World War II, Sellers was an airman in the Royal Air Force, rising to corporal, though he had been relegated to ground staff due to poor eyesight. His tour included India and Burma, although the duration of his stay in Asia is unknown, and he may have exaggerated its length. He also served in Germany and France after the war.

As a distraction from the life of a non-commissioned officer, Sellers joined the Entertainments National Service Association (ENSA), allowing him to hone his drumming and comedy. He occasionally impersonated his superiors, and his portrayal of RAF officer Lionel Mandrake in the film Dr. Strangelove may have been modelled on them.

He bluffed his way into the Officers Club using mimicry and the occasional false moustache, although as he told Michael Parkinson in the 1972 interview, occasionally older officers would suspect him. The voice of Goon Show character Major Dennis Bloodnok came from this period.

After his discharge and return to England in 1948, Sellers supported himself with stand-up routines in variety theatres whose impresarios needed to legitimise their business. Sellers telephoned BBC radio producer Roy Speer, pretending to be Kenneth Horne, a member of the radio show, Much Binding in the Marsh, to get Speer to speak to him. Sellers was eventually cast on The Goon Show with Spike Milligan, Harry Secombe and Michael Bentine. Sellers followed this with television work.

In the 1950s he also starred on two comedy records produced by George Martin before his fame with The Beatles: "The Best of Sellers" and "Songs for Swinging Sellers". Tracks on these such as "Party Political Broadcast" and "Bal-ham!! ..Gateway to the South", featured Seller's ability to use his flexible voice to enormous comedic effect.

In the first he very accurately imitates an empty and very typical British political speech, delivered by an equally empty but upmarket British politician. And in the second a very funny take-off of an American travelogue typical of the sort of thing UK cinema audiences had to sit through in the 1940s and 50s. There are many other very funny tracks on these records including "Trumpet Volunteer"..an interview with a typical 1950s pop singer and "Auntie Rotter" a take-off of a popular small children's radio programme at the time, "Listen with Mother"

Sellers's film success arrived with British comedies, including The Ladykillers, I'm All Right Jack and The Mouse That Roared. He began receiving international attention for his portrayal of an Indian doctor in The Road to Hong Kong, the seventh and last in the "Road" series, starring Bing Crosby, Bob Hope, Dorothy Lamour.

Sellers found further international acclaim with the The Millionairess with Sophia Loren. The film inspired the George Martin radio and television production Goodness Gracious Me, as well as two novelty songs Goodness Gracious Me and Bangers and Mash, both featuring Sellers and Loren. He starred in Stanley Kubrick's Lolita as Clare Quilty, opposite James Mason as Humbert Humbert. In portraying Quilty, Sellers proved a scene stealer.

A breakthrough came with Kubrick's Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb in which he portrayed three characters: U.S. President Merkin Muffley, Dr. Strangelove and Group Captain Lionel Mandrake of the RAF. Muffley and Strangelove appeared in the same room throughout the film. Sellers was also cast in the role of Major T. J. 'King' Kong.

Initially, Sellers struggled with the character's Texas accent, but screen writer Terry Southern made a recording of his own Texan accent, which Sellers apparently mastered after repeated listenings. However, during a scene in a plane designed for the set, Sellers fell 15 feet and broke his leg, preventing additional cockpit scenes and forcing Kubrick to replace Sellers with Slim Pickens.

Sellers is most famous for his performance as the bumbling Inspector Clouseau in the Pink Panther movies, a role that Peter Ustinov had declined. This character gave Sellers a worldwide audience, beginning with The Pink Panther and its sequel, A Shot in the Dark, in which he featured more prominently.

He returned to the character for three more sequels from 1975 to 1978. The Trail of the Pink Panther, containing unused footage of Sellers, was released in 1982, after his death. His widow, Lynne Frederick, successfully sued the film's producers for unauthorized use. Sellers had prepared to star as Chief Inspector Clouseau in another Pink Panther film; he died before the start of this project, Romance of the Pink Panther.

Sellers was a versatile actor, switching from broad comedy, as in The Party, in which he portrayed a bumbling Indian actor Hrundi Bakshi (an almost Indian version of Inspector Clouseau), to more intense performances as in Lolita.

Sellers faced a downturn by the early 1970s and was dubbed "box office poison". But after the successful return of Clouseau role in new Pink Panther movies, he produced and starred in a film, Being There (1979).

Based on the Jerzy Kosinski novel he cherished, Being There earned Sellers his best reviews since the 1960s, a second Academy Award nomination and a Golden Globe award. Sellers never won an Oscar but won the BAFTA for I'm All Right Jack.

Sellers appeared on The Muppet Show television series in 1977. He chose not to appear as himself, instead appearing in a variety of costumes and accents. When Kermit the Frog told Sellers he could relax and be "himself," Sellers (while wearing a Viking helmet, a girdle and one boxing glove, claiming to have attempted to dress as Queen Victoria), replied, "There is no me. I do not exist. There used to be a me, but I had it surgically removed."