He was the son and heir to Irish Gaelic lord Hugh O'Neill, Earl of Tyrone,[4] though he predeceased his father.

Dungannon accompanied his family and countrymen on the Flight of the Earls, leaving Ireland for mainland Europe.

A few months after settling in Rome, Dungannon became violently ill after catching fever during a holiday to Ostia.

[3] As the eldest son of Tyrone's second wife, Hugh was considered the heir to his father's titles and estates.

[19][4][18] In early July 1608, Dungannon travelled to Ostia, a coastal town fifteen miles west of Rome, for a holiday and change of air.

[20][19] Part of the inscription on his tomb (in Latin, translated to English) reads: "His lamentable death dashed the hopes which all had placed In him for his exemplary talents and distinction of soul and Body so propitious for a future favourable return to that Country once again.