Ua Briain, Conchobar (d. 1142) was a son of Diarmait Ua Briain (qv) (d. 1118) and of Mór, daughter of Domnall son of Gilla-Phátraic. Along with his half-brothers, Tairdelbach (qv) (d. 1167) and Tadc, he succeeded to the kingship on the death of his uncle, Muirchertach (qv), in 1119. The power assumed by the three siblings, however, was much reduced since Tairdelbach Ua Conchobair (qv), the Connacht ruler, had taken advantage of the conflict that beset Muirchertach's final years to increase his authority in Munster. Accordingly, even before his rival had drawn his last breath, he granted the southern half of the territory, Desmumu (Desmond), to Meic Carthaig, while the northern half, Tuadmumu (Thomond), was reserved for Conchobar and his brothers. Lest there be any misunderstanding as to who was actually in control, Ua Conchobair plundered Munster frequently in the following years, reimposing his bipartite division in 1121, according to the Annals of Tigernach (Tigernach Ua Bráein (qv)). Sandwiched in the middle, the Uí Briain brothers may initially have sided with their heavy-handed Connacht neighbour; having captured hostages proffered to Tadc Mac Carthaig, they handed them over to Tairdelbach in 1120. Yet as the decade progressed, an alliance with their more powerful Munster rivals was deemed more astute. Thus, in 1127, when Cormac Mac Carthaig (qv) was deposed by certain Munstermen, perhaps working in consort with the Connacht king, it was Conchobar and his brother, Tairdelbach, who restored him to political life, bringing him out of the monastery of Lismore and bestowing on him the kingship of Munster.
This seemingly magnanimous gesture set in train a period of fruitful cooperation that lasted a further seven years, during which time Conchobar Ua Briain gradually acquired the upper hand. On a hosting into Leinster in 1131 he acquired hostages, and made war on Connacht and Mide in the same year. Allied with Mac Carthaig, he attacked Connacht again (1133, 1134) before advancing against Diarmait Mac Murchada (qv) of Leinster with the support of the Osraige and the vikings of Waterford. By the time he turned his attention eastwards, the alliance with Meic Carthaig had ruptured, not least perhaps because the power of their common enemy, Ua Conchobair, had temporarily begun to wane. Sensing an opportunity, Ua Briain began to pursue an independent path, hostilities with his southern neighbours becoming commonplace. The two sides clashed in 1134 and again the following year. In a further encounter at Waterford (1137) Uí Briain were assisted by their former foe, Diarmait Mac Murchada. In the end, Conchobar emerged victorious not by means of military might but through treachery. In 1138 Cormac Mac Carthaig was slain in his own house by an ally of Uí Briain, Mathgamain Ua Conchobair Chiarraige, at the instigation of Conchobar's brother, Tairdelbach, the Annals of Tigernach claiming that it was in fact Tairdelbach himself who committed the terrible deed. As a result, Conchobar assumed the kingship of Munster.
The ambitious new king immediately set his sights on pastures further afield. In 1139 hostilities with Leinster were averted by the intervention of the archbishop of Armagh, who arranged a year's truce. Conchobar had greater success the following year when, on a hosting to Ardee, Donnchad Ua Cerbaill (qv), king of Airgialla, proffered hostages. One year later, he appears as the leader of those opposed to Tairdelbach Ua Conchobair. Significantly, his attack on Connacht was prefaced by a march into Dublin, where the kingship of the city was bestowed on him by its Ostmen inhabitants. It was one of the high points of his career; having contracted a mysterious illness he died in Killaloe within the year and was succeeded by his brother, Tairdelbach.