Cormac Mág Shamhradháin was a member of the McGovern clan who were the rulers in the Middle Ages of the tuath of Teallach n-Eachach in Breifne (now Tullyhaw, County Cavan, Ireland).
Cormac was subsequently ordained a priest and on 13 October 1461 he was appointed vicar of Templeport parish, County Cavan, in succession to Rory McGovern who had been excommunicated.
The Pope of course had already given Cormac dispensation for his illegitimacy when appointed bishop so the decision may best be viewed as a political struggle between the Lords of West Kilmore, the O’Rourkes, who backed the candidacy of their client sept of the McGoverns against the Lords of East Kilmore, the O’Reillys, who backed their client sept of the Bradys for the bishopric.
On 25 November 1482 Primate Octavian arranged a meeting between the two rivals at Inismor in Lough Gowna in order to come to a settlement.
[9] At the meeting, in return for certain payments from Tomás Mac Brádaigh, Cormac undertook to renounce all his emoluments from the two rural deaneries of Drumlane and Rossinver Dartry and also to refrain from seeking any further apostolic letters against the new bishop and to abide by the pledges given on his behalf by any nobles or poets.
"[11] An attempt to resolve the impasse was made at the Provincial Council of Armagh held in 1489 at St. Mary's Church, Ardee, County Louth under the presidency of Dr. John Payne, Bishop of Meath.
Bishop Tomás Mac Brádaigh died at Dromahaire, County Leitrim on Tuesday 29 July 1511 and was buried in Cavan Monastery on the following Friday 1 August 1511, with presumably Cormac in attendance.
[17] Diarmaid Ó Raghillaigh was then appointed as successor to Tomás Mac Brádaigh as the Bishop of Kilmore by Pope Julius II.
However Cormac Mág Shamhradháin was still claiming the bishopric so an appeal was made by the new Bishop Diarmaid to Pope Julius II to implement the decision of the 1489 Ardee Synod.
Before the Pope made his decision, Cormac died in December 1211 but as news to Rome travelled slowly in those days and the Vatican bureaucracy even slower, the word of his death had not reached the Pope by 3 June 1512 when Julius II issued a Bull which- "commanded the Bishop of Meath, and the Dean and Archdeacon of Kilmore, or any two or one of them, Cormac and any others evocandis being cited, if it should be evident to them then that in the matter adjudicated upon the sentence has been rightly given, to cause it by apostolic authority, appellatione postposita, to be firmly observed.
The Annals of Ireland for that year state- "Cormac Magauran, who was called Bishop in Breifny, died before Christmas".
Cormac left at least one son, Fergal Mág Shamhradháin, who continued the family traditions of priesthood and illegitimacy.