Guillaume du Desert was born at Paris about 1400.
He was nominated for a canonicate in the church at Rouen in 1421 by Henry V. On February 12, 1432, he took at Paris the degree of bachelor of law. He was in turn master of wills, from 1446 to 1448 master of work at the cathedral, which his family had endowed.

Guillaume du Désert fulfilled various missions which allowed him to think that he was a valuable man. He went to England to claim the payment of legacies that Henry V and Bedford had made to the cathedral.

He was absent from Rouen when Charles VII entered the city, and he obtained without trouble new letters of provision, and he undertook to get the King's confirmation of the Norman charter in 1452. The following year he fulfilled a mission to Rome. He was curé of Saint Nicolas le Painteur. Guillaume du Désert died on January 25, 1471, and was buried in the cathedral although he was curé of Saint Hilaire.

He was certainly an educated man, for he owned some fine books which he bequeathed to the Chapter library.

His decision in Jeanne's case was propped on that of the Abbot of Fécamp.
Guillaume du Désert was consulted among the first witnesses at the Rehabilitation proceedings: he had been present at Jeanne's abjuration and execution.

In his testimony he declared that he recalled very little about it, saying, for example, that "if Jeanne had taken the part of the English as she had that of the French she would not have been treated like that."