His father Tomás Óg 'na Fésóige' Mág Samhradháin, the Third, was chief of the clan until his death in 1458.
His half-brothers were Feidhlimidh Mág Samhradháin, the First his predecessor as chief, Tomás Óg, Brian, Maol Sheachlainn Dubh, Brian Caech, Tighearnán, Fearghal and Eóghan Mág Samhradháin also a chief of the clan.
In 1487 Domhnall Bernach was involved in a raid on Muintir Eolais in south County Leitrim but was captured by the McDermott clan.
Domhnall then tried to overthrow the McGovern chief, his half-brother Feidhlimidh Mág Samhradháin, the First, by enlisting the aid of the Maguire clan in his bid for the chieftainship and Feidhlimidh was captured by them on 2 June 1494 but released a few weeks later on 4 July.
Feidhlimidh had a stronghold on a crannog in Killywillin Lough and he met his death while there on Sunday 15 February 1495, possibly at the instigation of Domhnall who then took the chieftaincy and moved to the chief's residence in Ballymagauran.
The Annals of the Four Masters for 1495 state- Magauran (Felim, the son of Thomas, son of Brian Breaghach), Chief of Teallach-Eachdhach (Tullyhaw), was drowned in Loch-Crannoige of Caill-an-mhuillinn; and Donnell Bearnagh, his brother, took his place.