Írgalach (d. 702), son or grandson of Conaing (‘nepos Conaing’, AU; ‘mac’, according to some other annals) and a king of the Uí Néill, belonged to the dynasty of Síl nÁedo Sláine. His (grand) father, Conaing son of Congal, had been killed at the battle of Ogoman (662) while supporting the claims of his uncle Blathmac (qv) (d. 665) to the kingship of Tara. The name of his mother is not recorded, but he had at least two brothers, Dúngalach and Congalach. For his part, Írgalach married Muirenn (d. 748), a daughter of Cellach Cualann (qv) overking of Leinster, by whom he had a son, Cináed Cáech (qv).
It is probable that Írgalach was very young at the time of Conaing's death; he came to prominence only in the later 690s, after political power had rested with three of Conaing's first cousins in succession for more than thirty years. With the death of his brother Congalach (696), he was well placed to bid for headship of his dynasty, his main opponent being his second cousin, Niall son of Cernach Sotal, who had defeated Congalach eight years earlier. Írgalach's emergence as a political player coincided with a dynastic shift in relation to the kingship of Tara, as almost half a century of Síl nÁedo Sláine dominance had ended with the death of Fínshnechtae Fledach (qv) in 695 – when supremacy of the Uí Néill was claimed by Loingsech (qv) son of Óengus of Cenél Conaill. In 697 Írgalach was one of many dynasts to support the Law of Adomnán, which had been framed by Adomnán (qv), abbot of Iona, to protect women and non-combatants in time of war; other supporters of the initiative included Loingsech, Niall, and Cellach Cualann.
It seems ironic, therefore, that Írgalach and Cellach both appear in a negative light in Columban hagiography of the Middle Irish period; the Life of Adomnán (§5) implies that they (or at least their immediate descendants) were held in disdain by the Kells-Iona community. Perhaps the explanation lies in a shift of political loyalties sometime after the promulgation of the Law of Adomnán. Curiously, one version of the ‘Banshenchas’ (lore of women) claims that Írgalach's wife, Muirenn, had also married Loingsech, the Cenél Conaill dynast. As Írgalach predeceased Loingsech by a year and Muirenn is described in her obit as ‘Írgalach's queen’, it seems reasonable to infer a divorce, with a consequent slighting of the Iona-connected Cenél Conaill. There are difficulties in such an interpretation, however, as doubts may be cast on the testimony of the ‘Banshenchas’ in this regard. In any case, the designation of Muirenn as queen indicates that Írgalach held a royal dignity – whether or not Uí Néill subkingships, including that of Cnogba (Knowth) with which his dynasty was later associated, had yet assumed the familiar shape they had in Ireland's eighth-century political landscape.
There are hints that Írgalach threatened the re-established Cenél Conaill kingship of Tara, provoking a hostile reaction from Columban circles. Although not recognised as paramount ruler of Uí Néill either in the annals or in later king-lists, he is perhaps alluded to in the ‘prophecy section’ of the Old Irish regnal poem ‘Baile Chuinn’. There is reference to flaith hó Níell co Néll (sovereignty from Niall to Niall), understood by many as an allusion to Niall son of Cernach Sotal, but then comes less bes tres mí for bliadnai bebas muir (a month and a year [to] the one who will die by the sea) – which fits with Írgalach and the circumstances of his death. In 701 Írgalach slew his rival Niall, which may well have been viewed as a step towards consolidating his position in the midlands prior to a move against Loingsech. Besides, Niall had fostered connections with the Columban community of Kells, and the killing was seen as a breach of sanctuary. The biographer of Adomnán has the saint predict Írgalach's own violent death; a similar version of events is related in the Fragmentary Annals (§150, 153, 156).
The following year, Írgalach was killed on Ireland's Eye by a company of Britons, who were probably acting on behalf of Niall's lineage. His son Cináed Cáech obtained revenge in full in 724, when he defeated and killed Fogartach (qv) son of Niall, and seized the kingship of Tara, which his rival had claimed for the previous two years. Most of the later Uí Chonaing rulers of Cnogba descended, however, from Írgalach's nephew Amalgaid son of Congalach, who had assumed headship of the lineage in 702.