The Irish-born star began on the stage in Bristol and London aged 17, but his big break was when Sir David cast him as British adventurer T E Lawrence.
It earned him the first of eight Oscar nominations, with others coming for such films as Becket, The Lion in Winter and Goodbye, Mr Chips.
He received an honorary Oscar in 2003.
He had initially refused to accept the award.
In a letter he asked the Academy of Motion Picture Arts and Sciences to delay the award until he was 80, saying he was “still in the game and might win the bugger outright”.
Our thoughts and prayers go out to O’Toole’s family and friends at this difficult time.