A descendant of Diarmait Mac Murchada (died 1171), Domhnall was the eldest of the two sons of Donnchadh, lord of the Art Buihde Caomhánach sept, who were reckoned the least powerful of the dynasty. Their lands lay north of Enniscorthy in the Blackstairs Mountains. It appears that at Donnchadh's death, Domhnall was taken into the care of the seneschal of Wexford, Thomas Stukeley. When Stukeley left for Spain in 1568 Domhnall went with him, which explains the origin of his nickname, Spáinneach (Irish for Spaniard).