Sir Donnell O'Donnell (died 1590) was a member of the O'Donnell dynasty of Tyrconnell in modern-day County Donegal. He was the eldest son of Sir Hugh O'Donnell, the ruler of Tyrconnell for much of the reign of Elizabeth I. Shortly after the Armada shipwreck of 1588 he was appointed as Sheriff of Donegal by the Lord Deputy William FitzWilliam. Fitzwilliam also had Sir Eoin O'Gallagher, an influential supporter of Hugh Roe arrested and imprisoned. In 1589 a force of Irish Army troops were sent into the area under Captain John Connill who assisted Donnell against his rivals.