Son of Amlaib Mor Ua Donnchadha, king of Ui Echach and champion of Iarmumu.
He was vigorous chief and active fighter, leading a punishing raid into O’
Brian territory in 1177. This was after he had regained control of his sept
from his dead brother Cathal who had been killed by the Normans in their
initial invasion.

Domnaill also opposed the actions of Conchobar Ua Donnchadha of the Glen and
slew him in 1178. He in turn was killed by the O’Donoghue’s ancestral
enemies the O’Brians (Ui Chinaeda) in 1178.