Irish rebel who, from 1595 to 1603, led an unsuccessful Roman Catholic uprising against English rule in Ireland. The defeat of O'Neill and the conquest of his province of Ulster was the final step in the subjugation of Ireland by the English.

Although born into the powerful O'Neill family of Ulster, Hugh grew up in London. In 1568 he returned to Ireland and assumed his grandfather's title of Earl of Tyrone. By cooperating with the government of Queen Elizabeth I, he established his base of power, and in 1593 he replaced Turlough Luineach O'Neill as chieftain of the O'Neills. Skirmishes between Tyrone's forces and the English in 1595 were followed by three years of fruitless negotiations between the two sides.

In 1598 Tyrone reopened hostilities. His victory (August 14) over the English in the Battle of the Yellow Ford on the Blackwater River, Ulster—the most serious defeat sustained by the English in the Irish wars—sparked a general revolt throughout the country. Pope Clement VIII lent moral support to Tyrone's cause, and, in September 1601, 4,000 Spanish troops arrived at Kinsale, Munster, to assist the insurrection. But these reinforcements were quickly surrounded at Kinsale, and Tyrone suffered a staggering defeat (December 1601) while attempting to break the siege. He continued to resist until forced to surrender on March 30, 1603, six days after the death of Queen Elizabeth.

Elizabeth's successor, King James I, allowed Tyrone to keep most of his lands, but the chieftain soon found that he could not bear the loss of his former independence and prestige. In September 1607 Tyrone, with Rory O'Donnell, Earl of Tyrconnell (Tyrconnell, Rory O'Donnell, 1st Earl of, Baron Of Donegall), and about 100 northern chieftains, secretly embarked on a ship bound for Spain. The vessel was blown off course and landed in the Netherlands. From there the refugees made their way to Rome, where they were acclaimed by Pope Paul V. This “flight of the earls” signaled the end of Gaelic Ulster; thereafter the province was rapidly Anglicized. Outlawed by the English, O'Neill lived in Rome the rest of his life.