Duncan, who rose to prominence by playing a death row inmate in the acclaimed film The Green Mile, had suffered a heart attack in July. But he failed to recover from it.
A former bodyguard, the 6ft 4in Duncan was an imposing figure who played a wide variety of screen roles. He was nominated for an Oscar in 1999 for The Green Mile, but also played action roles and voiced animated parts.
Duncan will be remembered primarily for his role alongside Tom Hanks in the adaptation of Stephen King's novel The Green Mile. He played convicted murderer John Coffey, a man possessed of a gentle demeanour and extraordinary healing powers.
His unexpected performance won him a nomination as best supporting actor and kick-started an acting career that only began once he gave up bodyguard work in his 30s.