Initially, the Bishop of Orkney, William the Old, tried to suppress the growing cult of Magnus, dismissing the alleged miracles and warning that it was "heresy to go about with such tales".
But then, in an episode described in the Orkneyinga Saga, Bishop William was suddenly convinced of Magnus’ holiness after being struck blind in his Birsay cathedral.
Falling upon Magnus’s grave, and praying, the bishop’s sight was miraculously restored.
But intriguingly the bishop's change of heart seems to have coincided with a visit to Norway.
Although the saga makes no mention of the purpose of this journey, the historian William Thomson suggests that, in Norway, the bishop had met with the future Earl Rognvald - the man who would go on to found St Magnus Cathedral after the Orkney earldom became his.
If this were so, Bishop William's sudden promotion of the cult of Magnus could have had political reasons - Rognvald's plans to acquire the earldom centred on the popularity of the Magnus cult.
Whatever the reason, 21 years after their burial, Bishop William had Magnus’ remains exhumed, washed and tested in consecrated fire. Their holiness confirmed, Magnus was proclaimed a saint and his remains enshrined above the Birsay kirk's altar.
The relics stayed in Birsay "for a long time" until Magnus supposedly appeared to a Westray man, Gunni, in a dream. Magnus told Gunni that Bishop William should be told that Magnus wished to leave Birsay and move east to the growing town, Kirkjuvagr – the Kirkwall we know today.