William fitzHerbert was formally canonised by Pope Honorius III on 18 March 1226. The text of the papal bull was carefully preserved at York. Written in the verbose style of the papal bureaucracy, it declares, after a lengthy preamble, that the pope has entered William's name in the list of the holy confessors, so that his feast-day should be celebrated annually thereafter in solemn manner. The canonisation, it states, was proclaimed only after a careful investigation of the course of the most holy life of the saint and the many great miracles which the Lord had performed through him. Some of these are listed: oil flowing from the tomb which had healed many people of their infirmities; three dead people brought back to life; five blind people given their sight; and new eyes given to a man who had been unjustly defeated in a duel and blinded. But the papal canonisation was only the official culmination of a process which had taken place over the previous half-century in York, where William had been venerated as a saint since the late 1170s. It is this process which we now must trace.

The second half of the early-thirteenth-century Life of St William is dedicated to his miracles. It starts with the earliest recorded posthumous miracle, and recounts how fire broke out in the city and spread to the Minster. A huge burning beam fell on William's tomb and broke the grave-cover in half. The lower part of it fell away exposing the body of the saint to the burning timber. But to everyone's astonishment, the silk vestments were not in the slightest bit burnt, nor the body damaged, and a sweet smell of burning incense or the most precious unguent was observed. And loss was turned to gain, for the humble old church was replaced by a bright and lofty new one, by the help of God and the then archbishop. This refers to the new east end of the Minster constructed by Archbishop Roger of Pont l’Évêque. Work is believed to have begun soon after he took office in succession to William fitzHerbert in 1154, so the episode must date to the mid-1150s. As recounted, the story contains many features common to miracle stories: the untouched body, the odour of sanctity, the disaster which comes to be seen nonetheless as an act of divine grace.