He belonged to a leading
Gaelic family from
County Tipperary, who had a strong
ecclesiastical connection. His family, according to his statement, founded
Jerpoint Abbey in the later twelfth century. Little is known of his parents or his early life, but he was
Dean of Cashel at the time of his elevation to the
episcopal see in August 1254.
King Henry III opposed his appointment, on the ground that he was known to be friendly with "the King's enemies", some of whom were MacCerbaill's relatives, but this objection was overruled by
Pope Innocent IV. To secure his favour with the English Crown, Mac Cerbaill went to England in 1255 and did
homage to the King at
Winchester, the first of his many visits to the Royal Court, but despite his repeated assurances of loyalty to the Crown, it does not seem that Henry or his son
Edward I ever fully trusted him. Apart from the question of where his real loyalties lay, MacCerbaill had a practice of
consecrating bishops without asking for the King's consent, which naturally irritated the monarch. Keran was so harassed that he appealed to the protection of the Pope, who commended him to the care of King Edward of England. Later the Archbishop clashed with the entire Dublin administration, whom he
excommunicated in 1275 in a trivial dispute over whether the Crown authorities or the Archbishop should have the governance of the new
jail in
Cashel. After outraged protests from his opponents, in particular from
Fromund Le Brun, the
Lord Chancellor of Ireland, a compromise was reached in 1277 by which the Archbishop was given control of the jail, but his opponents were judged to be blameless. His conduct on this occasion seems to justify the description of him as "ambitious and power-hungry". He attended the final session of the
Second Council of Lyon in 1274. ==Attempt to introduce the common law system in Ireland ==