By Poitier's own account, he was born in Miami, Florida but spent his childhood in The Bahamas and later moved back to the United States. Poitier was born prematurely and was not originally expected to survive. He spent his early years on remote Cat Island, which had a population of 4,000 and no electricity.

At the age of 10, Poitier traveled to Nassau with his family. His family attended the Anglican and then the Catholic Church, and Poitier was also involved with local voodoo traditions. As he got older, he displayed an increasing inclination toward juvenile delinquency. At the age of 15, his parents shipped him off to Miami to live with his older brother. At age 17, Poitier moved to New York City and held a string of menial jobs. During this time, he was arrested for vagrancy after being thrown out of his housing complex for not paying rent, and decided to join the United States Army.

Poitier tried his hand at the American Negro Theater, where he was handily rejected by audiences. Determined to refine his acting skills and rid himself of his noticeable Bahamian accent, he spent the next six months dedicating himself to achieving theatrical success. On his second attempt at the theater, he was noticed and given a leading role in the Broadway production Lysistrata, for which he got excellent reviews. By the end of 1949, he had to choose between leading roles on stage and an offer to work for Darryl F. Zanuck in the film No Way Out (1950). His performance in No Way Out as a doctor treating a white bigot was noticed and led to more roles, each considerably more interesting and prominent than most black actors of the time were getting, though still less so than those white actors routinely obtained.

Poitier's breakout role was as a member of an incorrigible high school class in the 1955 film Blackboard Jungle. At age twenty-seven, like most of the actors in the film, he was not a teenager. Poitier was the first male black actor to be nominated for a competitive Academy Award (for The Defiant Ones, 1958), and also the first to win the Academy Award for Best Actor (for Lilies of the Field in 1963).

He acted in the first production of A Raisin in the Sun on Broadway in 1959, and later starred in the film version released in 1961. He also gave memorable performances in The Bedford Incident (1965), A Patch of Blue (1965) co-starring Elizabeth Hartman and Shelley Winters; Guess Who's Coming to Dinner (1967); and To Sir, with Love (1967). Poitier played Virgil Tibbs, a Philadelphia, Pennsylvania detective in the 1967 film In the Heat of the Night and its two sequels: They Call Me Mister Tibbs (1970) and The Organization (1971).

Poitier has directed several films, the most successful being the Richard Pryor-Gene Wilder comedy Stir Crazy, which for years was the highest grossing film directed by a person of African descent. His feature film directorial debut was the western Buck and the Preacher in which Poitier also starred in alongside Harry Belafonte. Poitier replaced original director Joseph Sargent. The trio of Poitier, Cosby, and Belafonte reunited again (with Poitier again directing) in Uptown Saturday Night. Poitier also directed Cosby in Let's Do It Again, A Piece of the Action, and Ghost Dad.

In April 1997, Poitier was appointed as ambassador of the Bahamas to Japan, a position he currently holds. He is also the ambassador of the Bahamas to UNESCO. Since 1998, he has been a Member of the Board of Directors of The Walt Disney Company.