Derbfhorgaill (c.1108–1193), daughter of Murchad and queen-consort of Bréifne, belonged to the Ua Máelshechlainn line of Clann Cholmáin. Her father Murchad Ua Máelshechlainn (qv) was a long-reigning (1106–53) but oft-expelled king of Mide; her mother Mór was a daughter of Muirchertach Ua Briain (qv), Dál Cais claimant to the high-kingship. Apparently born c.1108, Derbfhorgaill had two full-brothers: Domnall, promoted as king in 1127 in place of their father, and Máel-Sechlainn, who acceded to kingship of half of Mide in 1152. She also had three half-brothers – Conchobar (d. 1133), Art (d. 1141), and Donnchad ( fl. c.1144) – and a sister, Tailtiu (d. 1127), who married the Connacht claimant to the high-kingship, Tairdelbach Ua Conchobair (qv). Derbfhorgaill was also a cousin of Agnetha Ní Máelshechlainn (qv), abbess of Clonard.
Her father Murchad's reign at first seemed promising for Mide: he promoted the young Tigernán Ua Ruairc (qv) to the kingship of Bréifne in 1122, and Tigernán subsequently married Derbfhorgaill, probably while she was still in her teens. It is not stated that she was the mother of his son Áed Manach (slain 1171); she may, however, have been the mother of his son Máel-Sechlainn, on the grounds that this name is strongly associated with her family. In 1130 Tigernán helped to restore her father who had earlier been driven from Mide, but his defection to Ua Conchobair in 1138 helped to accelerate the decline of Clann Cholmáin. Tigernán and his sometime ally, Diarmait Mac Murchada (qv) overking of Leinster, were beneficiaries of a partition of Mide effected by Ua Conchobair in 1144; on the collapse of this arrangement a year later, however, her father Murchad defeated Ua Ruairc and secured support from Munster against Leinster.
Far from settling matters, this turn of events sharpened rivalries, and Derbfhorgaill found herself caught between the conflicting ambitions of her husband and those of her kin. Although the rivals joined forces against Ua Briain of Munster at Móin Mór (Mourneabbey, Co. Cork), her father was at this stage again in exile; his restoration in 1152, following which he shared Mide with her brother Máel-Sechlainn, provided the immediate backdrop that year for Derbfhorgaill's ‘flight’ with Mac Murchada. It is probable that her relationship with her husband had long been uneasy; no doubt she was tired of his constant changing of sides and at the same time she must have been anxious to halt the erosion of Clann Cholmáin power.
There would appear to be little justification for the past romanticisation of the episode which can scarcely be described as an ‘abduction’, much less an ‘elopement’. Given their ages (both were by all accounts in their forties) and their political involvements, it is hardly appropriate to picture the pair as ‘star-crossed lovers’. There is ample evidence in the ‘Song of Dermot’ and in the annals to suggest that Derbfhorgaill acceded to the arrangement. Encouraged, it seems, by Máel-Sechlainn, she invited Mac Murchada to a crannóg (in Meath, according to some accounts), and departed with him, taking her cattle and belongings. No force was involved, and she left with her personal wealth – presumably her original dowry. While the outcome for Ua Ruairc was dishonour (as almost certainly was intended), it seems reasonable to interpret the episode as an attempt to align Clann Cholmáin with Leinster and to block Bréifne expansion in the midlands.
It has been suggested by some that, during her year's absence in Leinster, she bore a daughter to Mac Murchada – the Derbfhorgaill who was later married to the son of Gilla-Mocholmóg – but there is no evidence for this; besides, she was probably past child-bearing age. In any event, in 1153 she was returned to her husband by Ua Conchobair, after he defeated Mac Murchada. Whether or not Derbfhorgaill felt any need to make amends for her part in this ‘liaison’, she certainly became a benefactress of the church. In 1157 she endowed the Cistercian foundation of Mellifont with three-score ounces of gold, a gold chalice and a number of altar-cloths. Ten years later, she was responsible for building the Nuns' Church at Clonmacnoise. In 1186 she entered religious retirement at Mellifont, where she died in 1193 at a venerable age, probably not far short of the eighty-five years traditionally ascribed to her.