[6] Domnall was a member of the Uí Briain, a branch of the Dál Cais, descended from the eponymous Brian Bóruma mac Cennétig, High King of Ireland.

[8] The fourteenth-century Annals of Tigernach accord Domnall the epithet gerrlámhach ("short-armed") which may indicate—if the term is taken literally—that he suffered some sort of deformity.

[11] In 1075, in an act of overlordship over the Kingdom of Dublin, Toirdelbach Ua Briain appointed Muirchertach Ua Briain King of Dublin,[12] following a precedent set by Diarmait mac Maíl na mBó, King of Leinster, a previous claimant to the Irish high-kingship who had done the same to his own eldest son, Murchad, in 1052.

[16] After the Gofraid's death the following year, Muirchertach Ua Briain appointed his own nephew, Domnall mac Taidc, as King of the Isles.

Although he may have been forcibly ejected by the Islesmen,[21] he may well have returned to Ireland to take advantage of Muirchertach Ua Briain's rapidly failing health.

The record of a grant to Christ Church Cathedral, in which Domnall is styled "King of Ireland", appears to suggest that he attempted to assert a claim to the kingship as well.

[25] In fact, the fifteenth-century Mac Carthaigh's Book specifically states that Domnall was installed in the kingship of Dublin by his father in 1114.

[26] Although Muirchertach Ua Briain's problems were lessened with the death Domnall mac Taidc in 1115,[27] within the year the co-kings of Leinster—Donnchad mac Murchada and Conchobar Ua Conchobair Failge, King of Uí Failge—took advantage of his own decline, and attempted to gain control of Dublin by way of a major assault upon the town.

[25] Unfortunately for Donnchad, however, he lost his life in the encounter;[34] and according to the thirteenth-century ecclesiast Giraldus Cambrensis, the Dubliners added insult to injury by burying his corpse with that of a dog as a show of contempt to the Leinstermen.

[49] Before the frail Muirchertach Ua Briain finally died in 1119, he was forced to resign the kingship of Munster in favour of his half-brother.