The legendary British actor fell ill at his home near Petersfield, in southern England, and was taken by ambulance to the King Edward VII Hospital, where he died Saturday, hospital spokeswoman Jenny Masding said Sunday night.
The cause of death was not released.
Mr. Guinness was one of the last surviving members of Britain's greatest generation of actors, which included Sir Laurence Olivier and Sir Ralph Richardson.
From postwar comedies through epics such as The Bridge on the River Kwai, and crowd-pleasers such as Star Wars, Mr. Guinness played a vast variety of characters with subtlety and intelligence.
But it was his role as the Jedi Obi-Wan Kenobi in Star Wars that won Mr. Guinness a new generation of fans and made him financially secure.
The line "May the Force be with you" perhaps was the thing most moviegoers remember him for today.
"I might never have been heard of again if it hadn't been for Star Wars," he said of his role.
He also reprised his Obi-Wan Kenobi role in the series' first two sequels.
He made his mark in films in the Ealing Studio comedies of the late 1940s and '50s: The Man in the White Suit, The Lavender Hill Mob, The Lady Killers and, most remarkably, in Kind Hearts and Coronets, in which he played 10 members of an eccentric English family.
In roles such as Fagin in Oliver Twist, Mr. Guinness was barely recognizable behind his makeup and costume.
But with The Bridge on the River Kwai in 1957, he established that his versatility had nothing to do with disguise. He won an Academy Award for his performance as the disciplined, inflexible Col. Nicholson in a World War II Japanese prison camp.
Three years later, he played Nicholson's opposite â€“ Jock Sinclair, a boorish, hard-drinking Scottish lieutenant colonel, in Tunes of Glory.
He once described it as his favorite film role â€“ "perhaps the best thing I've done," he said. Mr. Guinness had a long film partnership with director David Lean, beginning in 1946 as Herbert Pocket in Great Expectations, through Oliver Twist, The Bridge on the River Kwai, Doctor Zhivago and, finally, in A Passage to India in 1984.
Mr. Guinness did little television, but became John Le Carre's quiet spy George Smiley in Tinker, Tailor, Soldier, Spy (1979) and Smiley's People (1981).
Born April 2, 1914, Mr. Guinness was an illegitimate child who did not know the name on his birth certificate was Guinness until he was 14.
After scraping together the funds for elementary lessons, he won a place at the Fay Compton School of Acting. There, John Gielgud judged the end-of-term performance and chose him as the prize winner.
Mr. Guinness had some of his first stage roles in Mr. Gielgud's plays.
In one of them, Mr. Guinness met actress Merula Salaman, whom he married in 1938. They had a son, Matthew, and remained happily married, living in a country house in Petersfield.