DUBHDALETHE (d. 1064), was son of Maelmuire, son of Eochaidh, and had been ferleighinn or lector at Armagh in 1049, when, on the death of Amalgaidh, comharb or successor of St. Patrick, he succeeded to that dignity, thus being the third of that name who held it. He entered on his office on the day of Amalgaidh's death, which proves that the appointment was not made by popular election but on some other principle accepted and recognised by the clergy and people. The lectorship thus rendered vacant was filled by the appointment of Ædh o Forreidh, who had been for seventeen years bishop of Armagh. Sir James Ware, who terms Dubhdalethe archbishop of Armagh, finds a difficulty in the fact of Forreidh having been also bishop during his time. But the comharb of Armagh, or primate in modern language, was not necessarily a bishop, and in the case of Dubhdalethe there is even some doubt whether he was ordained at all. A bishop was a necessary officer in every ecclesiastical establishment like that at Armagh, but he was not the chief ecclesiastic. In 1050 Dubhdalethe made a visitation of Cinel Eoghain, a territory comprising the county of Tyrone and part of Donegal, and brought away a tribute of three hundred cows. In 1055, according to the ‘Annals of Ulster,’ he made war on another ecclesiastic, the comharb of Finnian, by which is meant the abbot of Clonard, in the south-west of the county of Meath. A fight ensued between the two parties, in which many were killed. The quarrel probably related to some disputed property belonging to one or other of the abbeys concerned. This entry is omitted by the ‘Four Masters,’ according to a practice not unusual with them of suppressing inconvenient facts.
In 1064 they record his death, and add that ‘Maelisa assumed the abbacy.’ Thus the duration of Dubhdalethe's primacy was fifteen years. Ware, however, states that, according to the ‘Psalter of Cashel,’ it was only twelve, ‘which,’ he says, ‘affords some room to suspect that Gilla Patrick MacDonald, who is expressly called archbishop of Armagh in the “Annals of the Four Masters” at 1052, ought to intervene between Amalgaidh and Dubhdalethe, which will pretty well square with the death of the latter in 1065 .’ But in fact Gilla Patrick is only termed prior by the ‘Four Masters,’ and more exactly by the ‘Annals of Ulster,’ secnab or vice-abbot. St. Bernard of Clairvaux, in his ‘Life of Maelmogue or Malachy, Primate of Armagh’ (1134–7), refers in severe terms to the usage ‘whereby the holy see [Armagh] came to be obtained by hereditary succession,’ and adds, ‘there had already been before the time of Celsus (d. 1129) eight individuals who were married and without orders, yet men of education.’ One of these must have been Dubhdalethe, but St. Bernard was in error in viewing the influence of the hereditary principle at Armagh as unusual. The comharbs of St. Finnian, St. Columba, and other famous saints succeeded according to certain rules in which kinship to the founder played an important part. And thus it was that Dubhdalethe succeeded his predecessor on the day of his death, and that Maelisa, on the death of the former, ‘assumed’ the abbacy.
Dubhdalethe was the author of ‘Annals of Ireland,’ in which he makes use of the christian era. This is one of the earliest instances in Ireland, if we accept O'Flaherty's opinion, that it only came into use there about 1020. He considered him as contemporary with Mugron, abbot of Hy (d. 980), and as he must therefore have been at least sixty-nine years old when he became primate, and may naturally be presumed to have compiled his ‘Annals’ at an earlier period, he may have been actually the first to use it. His ‘Annals’ are quoted in the ‘Annals of Ulster’ (1021), p. 926, and in the ‘Four Masters,’ p. 978. He is also reported to have been the author of a work on the archbishops of Armagh down to his own time.[O'Conor's Scriptt. Rer. Hib. iv. 290; Annals of the Four Masters, ii. 587, 887; Ware's Works (Harris), p. 50; Colgan's Trias Thaum. p. 298 b; Lanigan's Eccles. Hist. iii. 428, 448.]