Gormlaith (d. 948), daughter of Flann Sinna and queen consort in turn of Munster, Leinster, and Tara, belonged to the Southern Uí Néill dynasty of Clann Cholmáin. Her father Flann Sinna (qv) was king of Tara, and her mother (also named Gormlaith) was a daughter of the Síl nÁedo Sláine ruler Flann son of Conaing. Gormlaith daughter of Flann Sinna had seven brothers or half-brothers, the most prominent of whom was Donnchad Donn (qv) who became king of Tara; the others included Máel-ruanaid (slain 901 by the Luigne), Conchobar (d. 919), and Domnall (d. 921). She also had at least one sister, Lígech, who married Máel-mithig of Síl nÁedo Sláine and was the mother of the latter's son Congalach Cnogba (qv).
Gormlaith is credited with having contracted three successive dynastic marriages. There is a strong tradition, reflected in the late Middle Irish poem ‘Éirigh [a] ingen an rígh’, that her first husband was the cleric-king of Cashel, Cormac (qv) son of Cuilennán. At the same time, it is stressed that Cormac was a celibate and their marriage was merely a symbolic union. It is distinctly possible that her relationship with Cormac, who fell at the battle of Belach Mugna (barony of Idrone, Co. Carlow; 908), is a fiction – created when the memory of Gormlaith became assimilated to the ‘sovereignty goddess’ who had three husbands.
There is a stronger case for accepting as historical Gormlaith's marriage to Cerball (qv) son of Muirecán, the Uí Fháeláin king of Leinster who defeated and slew Cormac. That being so, she was perhaps married to Cerball for longer than the single year between the battle and his own death. One version of events, outlined in a Book of Leinster text, has Cerball as her second husband and portrays him as a boorish character who insulted the memory of Cormac and at times behaved so violently towards her that on at least one occasion she was obliged to return to her father. A ‘Dindshenchas’ (topographical lore) poem (also in the Book of Leinster), however, presents another view of their relationship. Here, Gormlaith is blamed for the deaths of Cellach Carmain (seemingly an Uí Muiredaig rival of her husband) and his wife Aillenn. The implication is that she helped to further Cerball's political ambitions, which fits better in the context of a marriage-alliance with Uí Fháeláin which pre-dated Belach Mugna. Some time after Cerball's death (909), Gormlaith married Niall Glúndubh (qv) of Cenél nÉogain, who succeeded to the kingship of Tara and was killed in the battle of Islandbridge (919). Although it emerges from later poems that she had at least one son, she was ostensibly not the mother of Niall's son Muirchertach na Cochall Craicinn (qv).
According to medieval sources, Gormlaith was a poetess in her own right and composed laments for her husbands Cerball and Niall. Various verses, ranging in date of composition, were assigned to her by still later authorities. Presumably, this development gave rise to the folk tradition, related in the Annals of Clonmacnoise and repeated by several modern commentators, that Gormlaith was left destitute by her royal husbands and became a wandering poet dependent on the support of common people. It may be noted that her obit in the usually reliable Annals of Ulster says nothing of her alleged role as a poet. The fact that she outlived her second (or third) husband by almost thirty years suggests that Gormlaith attained a relatively advanced age. She died in penitence, which perhaps indicates that she had assumed the habit of a nun.