Their southern territory became known as Fir Cell (land of the churches) covering a large part of what is now County Offaly, where the surname O'Molloy is still very common.
In Lent 1186, when John Comyn, archbishop of Dublin, held a synod at Holy Trinity Church, O'Molloy preached a long sermon on clerical continency, in which he laid all the blame for existing evils on the Welsh and English clergy who had come over to Ireland.
In 1205, O'Molloy received 10 shillings from the royal gift, and on 3 April 1206 was recommended by the king to the chapter of Cashel for archbishop.
King Henry III begged the bishop to absolve the dead, but O'Molloy refused to do so unless restoration were made.
To this the younger William Marshal and his brothers refused their consent, and O'Molloy then cursed them, and foretold the end of their race.
His interest in the saint partly stemmed from the fact that Mag Arnaide lay within the diocese of Ferns, but also denoted his personal attachment to the saint's cult in an episode where Abbán converts a man of royal rank from the area and baptises his son: "I who gathered together and wrote the Life am a descendant [nepos] of that son".
O'Molloy consecrated the infirmary chapel at the Cistercian abbey of Waverley on 6 November 1201, and dedicated five altars there on 10 July 1214.