Irish chieftain, alternately an ally of and rebel against the English.

Grandson of Calvagh O'Donnell (through his son Conn), he was incensed at the elevation of his cousin Hugh Roe O'Donnell (O'Donnell, Hugh Roe) (q.v.) to the chieftainship of the O'Donnells in 1592 and was further alienated when Hugh Roe deprived him of his castle of Lifford; a bitter feud between the two O'Donnells was the result. Niall Garve made terms with the English government, to which he rendered valuable service both against the O'Neills and against his cousin. But in 1601 he quarrelled with the lord deputy, who, though willing to establish Niall Garve in the lordship of Tyrconnell, would not permit him to enforce his supremacy in Inishowen. After the departure of Hugh Roe from Ireland in 1602, Niall Garve and Hugh Roe's brother Rory went to London, where the privy council endeavoured to arrange the family quarrel, but failed to satisfy Niall. Charged with complicity in Cahir O'Dogherty's rebellion in 1608, Niall Garve was sent to the Tower of London, where he remained until his death in 1626.