He was thought to be related to King Stephen of England, who helped to secure his election to the province after several candidates had failed to gain papal confirmation.
He did not hold the province long, dying shortly after his return, allegedly from poison in the chalice he used to celebrate Mass.
[8] The influence of his rich and powerful father, who had many landholdings in Yorkshire, may have been of benefit in gaining him these offices at a relatively early age.
Sully's election was opposed by Pope Innocent II,[13] who refused to confirm him as Archbishop while he remained Abbot of Fécamp.
[16] Theobald of Bec, the Archbishop of Canterbury, refused to recognise William's election due to allegations of simony (acquisition of church positions by bribery), and of interference by King Stephen.
[17] In 1143, Pope Innocent II ruled that William could be confirmed in office if he swore under oath that the allegations were false.
After he swore the oath, Henry of Blois, who was also papal legate, found William innocent, and he was consecrated as archbishop on 26 September 1143.
[5][15] While awaiting the final decision in his case, William took up residence with one of his friends, Roger II, King of Sicily.
[19] Hearing of his suspension, some of William's supporters in York launched a damaging attack on Fountains Abbey, which destroyed many of the buildings.
Stephen probably wished to trade recognition of Murdac for support for his son Eustace, whose coronation as his successor he was trying to secure during his own lifetime, to defeat rival claims to the throne by Henry of Anjou.
[22][b] Within a few years both Murdac and the Pope had died and William travelled to Rome to plead with the new Anastasius IV for restoration to office.
[24] After less than a month back in York, William died on 8 June 1154,[12] allegedly due to poison administered in the chalice at Mass.
[25] William was buried in York Minster[26] and within a few months of his death, miracles were attributed to his intervention and a sweet smell came from his tomb when it was damaged during a fire.
[28] Although his veneration was largely localised in York, among his devotees was Margery Kempe (1373–1438) of King's Lynn in Norfolk, who "cried copiously" before his tomb.
The tomb shrine was built c. AD 1330 on the site of William's original burial place in the eastern-most bay of the nave; it comprised a large stone or marble slab five or six feet in height supported by a series of decorative arches (four on the longer sides, two on the shorter) with an upper stage of decoration rising above it.
A lead ampulla found in York and depicting an archbishop on one side has been argued to represent Saint William.
[33] In the 1890s Catholic pilgrims who were part of the Guild of Our Lady of Ransom pilgrimage through York were given permission to kiss the shrine.
In 1715 Ralph Thoresby reported that he had acquired some architectural fragments in marble which had been 'enclosed betwixt two walls and in a private House' from Precentor's Court.
[34] Several fragments from 18th century interventions at or near this house were later discovered spread around York including in the gardens near Clifford's Tower and used as domestic furniture.