Ua hAingliu, Donngus (Donatus) (d. 1095), third bishop of Dublin, was elected several months after his predecessor Patrick (qv) was drowned in the Irish Sea (10 October 1084). It would seem that Donngus was selected at a general synod as there is a reference to his being chosen by Tairdelbach Ua Briain (qv), overlord of Dublin and claimant to the high-kingship, together with the bishops of Ireland and the clergy and people of Dublin. He had been a Benedictine monk at Canterbury and was consecrated there in August 1085 by Lanfranc, archbishop of that see. He took a formal oath of obedience to Canterbury, but it may be significant that Lanfranc chose on this occasion not to style himself Britanniarum primas (primate of the Britains). Nonetheless, on his return to Dublin, Donngus carried with him letters of exhortation to the kings and clergy of Ireland advocating church reform, and a consignment of books, vestments, and church ornaments – gifts from Lanfranc for the cathedral of the Holy Trinity.
During the pontificate of Donngus (if not, indeed, earlier), monks were brought from Canterbury to form a new cathedral chapter. It may be safely assumed that he pursued reformist policies, but the Dublin of his day witnessed considerable political disruption. With the death of Tairdelbach (1086), the Ua Briain rulers temporarily lost control of the city, and the Uí Chennselaig king Donnchad, son of Domnall Remur (qv), came to prominence. Donnchad conveyed the site of Cluain Caín (Clonkeen, Blackrock, Co. Dublin) to Donngus's cathedral of the Holy Trinity. A restoration of Ua Briain power was followed by the intrusion of the Manx king Gofraid Méranach (qv) for the three years preceeding 1094. Perhaps it was knowledge of the political difficulties facing the reformers that prompted the new archbishop of Canterbury, Anselm, to address Donngus and Bishop Domnall Ua hÉnna (qv) in 1094, exhorting them to maintain their efforts for reform. Donngus died of plague on 22 November 1095; his successor in the see was his nephew, Samuel Ua hAingliu (qv).