William of St Calais (Carilef) (d. 1096), Bishop of Durham and chief counsellor of William Rufus, was a Norman monk and prior of St Calais in Maine, who received the see of Durham from the Conqueror in 1081.

In Durham annals he is honourably remembered as the prelate who designed the existing cathedral, and also for his reform of ecclesiastical discipline. His political career is less creditable. Honoured with the special confidence of William Rufus he deserted his patron's cause at the first sign of rebellion, and joined with Odo of Bayeux in urging Duke Robert of Normandy to claim the crown in 1088.

After the collapse of this plot William was put upon his trial before the Great Council. He claimed the right to be judged by his fellow bishops alone; this claim being rejected he appealed to the see of Rome. This was the first case of an appeal to the pope from an English tribunal which had occurred since the 7th century. Rufus and Lanfranc did not venture to dispute the right of appeal, but contended that the bishop, as a royal vassal, could not appeal against the forfeiture of his temporalities.

These were confiscated, and William left the kingdom, but no more was heard of his appeal, and in 1091 he regained the royal favour and his see. Thenceforward he showed the utmost subservience. He managed the king's case against Anselm, and at Rockingham (1095) actually claimed the right of appeal, when it was claimed by the archbishop. Notwithstanding his zeal for the royal interests, William was soon afterwards disgraced. He died in January 1096.