Lewis was born into a vaudeville family, and, at age 12, he developed a comedy act in which he mimed to records. He dropped out of high school in order to perform his speciality in New York City theatres, burlesque shows, and nightclubs. He first met singer Dean Martin in 1944, and two years later they officially became a performing team. Their act consisted of Martin singing, Lewis clowning, and both joining forces for a rousing finale of music and comedy. Well-received performances in Atlantic City and at New York City's Copacabana nightclub resulted in an offer from Hollywood.

After making Pardners (1956), Martin and Lewis had a much-publicized falling out and dissolved their partnership. Lewis then began a series of solo comedies, starting with The Delicate Delinquent (1957). Though he worked with such directors as Frank Tashlin and Norman Taurog, Lewis directed the majority of his films himself. Many of his pictures employed the formula of loose strings of gags and routines centred around Lewis's bungling character in a new job, such as the title character in The Bellboy (1960), a Hollywood messenger in The Errand Boy (1961), and a handyman at a girls' school in The Ladies' Man (1961). His comedy version of the Jekyll and Hyde story, The Nutty Professor (1963), opened to good reviews and is generally considered to be his best film.

After Which Way to the Front? (1970), Lewis did not appear in another film for 11 years, though he did film the unreleased The Day the Clown Cried in 1972. He continued to host an annual Labor Day telethon for the MDA, something he had been doing since 1966; during the 1976 show, Frank Sinatra (Sinatra, Frank) surprised Lewis by bringing Dean Martin onstage for a brief but electrifying reunion.

Lewis returned to the screen in 1981 with the episodic comedy Hardly Working. However, most of the critical accolades he would receive in the next two decades would be for dramatic or offbeat performances. He essayed acclaimed supporting roles in Martin Scorsese's The King of Comedy (1983), in the dramatic television series Wiseguy (1988–89), and in the film Funny Bones (1995). A longtime cult figure in France, Lewis was awarded that country's Order of Arts and Letters and the Legion of Honour in 1984. A successful revival of the musical Damn Yankees gave Lewis his first taste of Broadway success in 1995.