Ua Briain, Domnall Mór (‘the great’) (d. 1194) was a son of Tairdelbach Ua Briain (qv) (d. 1167) and of Sadb, daughter of Donnchad (qv) son of Gilla-Phátraic, king of Osraige. Dynastic warfare followed his father's death: Muirchertach, another son of Tairdelbach, being slain by a kinsman, Conchobar Ua Briain, who was in turn murdered by another relative, Diarmait Finn Ua Briain. Domnall Mór emerged victorious, becoming king in 1168, though it was not until he blinded his brother Brian later that year that he assumed overall control. Ruaidrí Ua Conchobair (qv) attempted to curb his authority, marching into Munster with his ally, Tigernán Ua Ruairc (qv), on Domnall's accession, with the intention of dividing the region between Mac Carthaig and Ua Briain. Yet the Munsterman too had powerful friends, having married Órfhlaith, daughter of Diarmait Mac Murchada (qv), around this time. In 1170 his father-in-law proved his loyalty, sending Anglo-Norman forces to Domnall's aid when he was attacked once more by the Connacht king. But Mac Murchada's death the following year left the Munster ruler vulnerable and Ua Conchobair was quick to take his hostages. Soon afterwards, however, on the arrival of King Henry II (qv) in Ireland later that year, the balance of power shifted again, Domnall and his Mac Carthaig neighbour immediately submitting to him. In so doing, as Marie-Therese Flanagan has observed, these southern kings were publicly rejecting Ua Conchobair's high-kingship, the Connacht ruler being in no position to protest (Irish society, 226–7).
Notwithstanding this, Domnall appears to have had the cooperation of Ua Conchobair three years later when, along with Ruaidrí's son, Conchobar Máenmaige Ua Conchobair (qv), he inflicted a heavy defeat on the Anglo-Normans at the battle of Thurles. This was Domnall's second such attack; he had demolished the Anglo-Norman garrison at Kilkenny the previous year. At the same time, the Munsterman was also at war with his own kin, blinding his half-brother, Mathgamain, as well as Diarmait, son of Tadc Ua Briain, in 1175. Ruaidrí Ua Conchobair was quick to intervene, taking the opportunity to depose Ua Briain and install his own candidate in his stead. In addition, at his instigation, Limerick was plundered by the Anglo-Normans, who established a garrison there, and the Connacht king seized the hostages of Thomond later that year. Despite this, he was unable to retain control in the region, Domnall and Ruaidrí making peace the following year. Moreover, on the death of Strongbow (Richard de Clare (qv)) later that year the Anglo-Normans abandoned Limerick to Ua Briain; in a gesture of defiance, he immediately set fire to the city. His authority there remained secure: the Anglo-Normans did not retake Limerick till after his death.
That Limerick was perceived by Domnall as his heartland is indicated by his use of the title ‘king of Limerick’ in charters, as Flanagan has noted (Irish society). These include one in favour of the Cistercians at Holy Cross abbey, significantly located some distance from Thomond in the territory of what was once the Éoganachta of Cashel. He was also associated in particular with the church of St Flannán (qv) at Killaloe where his brother, Consaitín, was bishop from 1179 till 1194, the year in which Domnall died. On his death, he is described as rí Muman (king of Munster) in the Annals of Inisfallen, in recognition perhaps of his attempts to consolidate and extend outwards from his base in Thomond. Moreover, north Munster was certainly stronger in Domnall's time than during the reign of his father, whose kingdom was in effect destroyed at the battle of Móin Mór. This situation was not to last, however, as a succession dispute between Domnall's three sons weakened the Uí Briain again in the aftermath of his death.