Probably following his family in the variety circuit, Sellers learnt this popular yet difficult art and the immediate instinct of the "gag". He was an incredibly versatile artist: an excellent dancer, a drummer good enough to tour with several jazz bands, and a skilful player of the ukulele and banjo (family legend has it that Seller's father actually taught George Formby to play the ukulele). He is known to have performed at the Windmill Theatre.

During World War II, Sellers was an airman in the Royal Air Force, rising to corporal by the end of the war. During his leisure periods, he did impersonations of his superiors. This helped Sellers in his later film Dr. Strangelove.

His success was quite slow in coming. He phoned up a television producer pretending to be Kenneth Horne, who was currently in the show Much Binding in the Marsh, in order to get them to speak to him. Success came as one of the Goons on the radio programme The Goon Show with fellow comedians Spike Milligan, Sir Harry Secombe and Michael Bentine and was followed by early television work.

Sellers' first film successes were in British comedies, including The Ladykillers (1955), I'm All Right Jack (1959) and The Mouse That Roared (1959). However, he is most famous for his role as the bungling Inspector Clouseau in the Pink Panther movies, which gave him a worldwide audience. He would play the character in four sequels between 1964 and 1978. The Trail of the Pink Panther was released posthumously in 1982, containing previously unused footage of Sellers. His widow Lynne Frederick later successfully sued the film's producers.

Sellers was launched internationally with the hit The Millionairess. His portrayal (or caricature) of Asian characters though, here and elsewhere, has caused some controversy in recent years. In Stanley Kubrick's Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb he notably played a triple role, comprising U.S. President Merkin Muffley, Dr. Strangelove, and Group Captain Lionel Mandrake of the RAF (the first two appearing in the same room throughout the film). Sellers was also cast in the role of Major T.J 'King' Kong. However, he was unable to master the Southern drawl Kubrick wanted for the role and Slim Pickens played it instead.

He was remarkably versatile, switching easily from broad comedy as in The Party, to more intense performances, as in Lolita, where he played Clare Quilty, the nemesis of the film's (and novel's) principal protagonist, Humbert Humbert.

Sellers' career had slumped by the early 1970s, but, after reviving the Clouseau character, he was able to produce his cherished project Being There in 1979, winning his best reviews since the 1960s. This, his last great film, brought him his second Academy Award nomination. He was unsuccessful on both occasions, although he did win a British Academy Award (BAFTA) for I'm All Right Jack. With Sophia Loren Sellers also recorded the top 10 UK single, Goodness Gracious Me.

Commonly considered a master actor and sometimes described as an "obsessive perfectionist", Sellers found in Blake Edwards a devoted director who could delicately underline and follow his comic rhythms. Edwards defined Sellers as a "mercurial clown" who could turn comedy into drama, and vice-versa, in an instant. He could also be cruel, as he demonstrated in his treatment of actress Jo Van Fleet on the set of I Love You, Alice B. Toklas, when she made a slight faux pas and offended him.

Sellers had casual friendships with two of the Beatles, George Harrison and Ringo Starr. Harrison told occasional Sellers' stories in interviews, and Starr appeared with him in the anarchic movie The Magic Christian, whose theme song was Badfinger's cover version of Paul McCartney's Come and Get It. Starr also gave Sellers a rough mix of songs from the Beatles' White Album, and the tape was auctioned (and bootlegged) after his death.

Sellers was also a close friend of Princess Margaret. Another interesting trait was his love for cars: he was believed to have owned and sold many different models by the 1960s. This was briefly parodied in a fleeting cameo in the short film Simon Simon, which was directed by his friend Graham Stark.

Sellers was the first man to appear on the cover of Playboy — he appeared on the April (1964) cover with Karen Lynn.

Sellers played ukulele-banjo on the New York Girls track for Steeleye Span's 1975 album, Commoner's Crown.