William de St. Carileph was so named from the borough and Abbey of St. Calais (alias St. Carilephus) on the southern border of Maine, where he either was born or took his first vows as a Benedictine. He was consecrated at Gloucester by Thomas Archbishop of Canterbury, in the presence of William the Conqueror and all the bishops of the Realm. He had been Abbot of St. Vincent's, in Normandy; and was, according to Simeon of Durham, "very sharp in his mind, subtle in his advice and, at the same time, of great eloquence and wisdom." William made him Grand Justiciary of England; and the privileges and possessions of the see of Durham were confirmed to Carileph after Pope Gregory VII had issued a bull for the full re-establishment of the see, the land of which had suffered greatly during the troubles of the Conquest.

Carileph himself asserts that he found his new bishopric "almost desolate". He relocated the monks from Wearmouth and Jarrow to Durham and, ten years later, began the massive task of erecting the vast cathedral which we see there today. The removal of Bishop Eldhun’s old Saxon building, was perhaps rendered necessary by the introduction of the monks and by the additional space which they required, or possibly just by the usual Norman love of construction.

In the mean time, however, the Bishop had joined the Norman nobles in supporting the claims of Duke Robert against those of the new king, William Rufus, and had been compelled to take refuge in Normandy. The castle of Durham and the temporalities of the see were seized for the King; and it was not until three years had passed that, in 1091, a reconciliation was effected, and the Bishop was returned to his see, bringing with him, as is very probable, the plans for his new cathedral. At the time of his death, it would appear that the work had advanced as far as the transepts.

The monks regarded him with great affection; and Simeon, who knew him personally, commends him highly: "he embraced the monks as the sweetest father would his dearest sons. He protected them, he cared for them and ruled with the utmost discretion".

Carileph again fell under King William’s displeasure and was summoned to his palace at Old Windsor, whither he travelled with much difficulty, suffering from great sickness. He died soon after his arrival on 6th January 1095. The monks and bishops who were present at his death-bed desired him to permit his burial within the walls of his cathedral church. However, no grave had as yet been made within the building which contained the incorrupt body of St. Cuthbert; and Carileph, rejecting the proposal, desired to be buried on the north-side of the chapter-house. After the death of Carileph, the see remained vacant for three years.