Ua Longargáin, Donnchad (Dionisius) (d. 1216), archbishop of Cashel, belonged to an ecclesiastical lineage of Dál Cais, descended from Donn Cuan, son of Cennétig. Earlier members of the family included Annad (d. 1099), abbot of Terryglas, Domnall (d. 1158), archbishop of Cashel, and Tadc (d. 1161), bishop of Killaloe. Donnchad, archbishop of Cashel, c.1208–1216, and his like-named successor are confounded by Watt, whose account of the prelate ‘Do[m]nal’ causes further confusion with a predecessor of half a century earlier. Donnchad was elected to a vacant see as successor to Muirges Ua hÉnna (qv) (d. 1206), against the wishes of the English crown. Previously King John (qv) had written to Thomas the archdeacon, to the suffragan bishops of the province, and to the justiciar, Meiler fitz Henry (qv), stating his approval of another candidate, the bishop of Ferns, Ailbe O'Mulloy (qv) (Ua Máel Muaid). Archbishop Donnchad found himself struggling against the Anglo-Norman interest, but countered by pursuing his claims at the papal court. By 1210, he had secured the pallium, along with confirmation of the possessions of his see and of the dioceses under his metropolitan jurisdiction.
Gradually a modus vivendi was worked out between the archbishop and the English administration in Ireland. In 1214 Donnchad was requested by the king to support the preferment of Geoffrey Albus, litteratus (man of letters), to the see of Cork, although, as there was no vacancy there at the time, Cloyne or Ross may have been intended. Whatever support Donnchad lent to the cause of Geoffrey, who in any event failed to be elected, is not recorded, but he does appear to have gained the gratitude of King John. The following year, while preparing for a pilgrimage to Jerusalem, he was granted a royal mandate for the protection of his free tenements, his tenants, and possessions. He also received from the English crown confirmation of a grant from the Dál Cais king of Thomond, Donnchad Cairprech O'Brien (qv) (d. 1242), of five holdings in that province. He set out on his journey, but died at Rome in early to mid-summer 1216.
His successor, a kinsman also named Donnchad Ua Longargáin (d. 1232), a Cistercian, was elected within months. His archiepiscopate was marked by bitter disputes with the English administration, as relationships deteriorated because of the decline of King John's authority in England before his death in October 1216. The second Archbishop Donnchad faced a crisis as the justiciar, William Marshal (qv), and Geoffrey Marsh, administrator of the Butler properties in Munster, took advantage of Henry III's minority to increase their power. Following the seizure of archiepiscopal property in the town of Cashel for the building of a castle, and the failure of complaints to king and pope regarding this action, Donnchad betook himself to France, placing the archdiocese under interdict. His self-imposed exile exacerbated the situation, as the Marshal interest, in collaboration with the English papal legate, Henry (qv) of London (archbishop of Dublin), secured the appointment of colonial nominees to the vacant sees of Killaloe and Ardfert. Protests to Rome by Donnchad were instrumental in securing papal judgments against these appointments, and the eventual replacement (in summer 1220) of Archbishop Henry as legate. However, as the English lobby in Rome gained in strength, Donnchad came under pressure and, in May 1222, was ordered to lift his interdict on Cashel. He did so, but appears to have harboured misgivings; he resigned his see before August 1223, and withdrew to a monastery, to be succeeded as archbishop by Mairín (Marianus) Ó Briain (qv). He died in retirement in 1232.