He was a son of Donall Mor O'Donnell (Domhnall Mór Ó Domhnaill), king of Tyrconnell (died 1241),[1] a man who was married to Lassarina (Lasairfhíona), daughter of Cathal Crobhdhearg Ó Conchobhair, King of Connacht.
The following year, Maurice FitzGerald invaded Tyrconnell, seizing several hostages and secured them within Sligo Castle.
[3] The year afterwards, O'Donnell counter-attacked FitzGerald, and the hostages were killed in retaliation.
[6] Following O'Donnell's death, FitzGerald installed Rory O'Cannon (Ruaidhrí Ó Cannanáin) as king of Tyrconnell.
[7] O'Donnell is the subject of a contemporary elegy composed by Giolla Brighde Mac Con Midhe (died c.