Until the 19th century, they were primarily thought of as an uncle and a nephew until the archivist Jules Doinel, based on historical documents, proved they were indeed father and son.
Guillaume was a student at the University of Orléans where he graduated as a Licencié ès lois; his father funded his education with the property he owned in Beauce, which was taken from the Burgundian Faction.
He received the duty of Grand Maistre Gouverneur and judge of the mines and outbuildings, and then Chancellor and Chamberlain of the Kings Charles VII and Louis XI.
[1] He stayed loyal to his king during the Ligue du Bien public in 1465, and for this, Louis XI rewarded him with an increase in his pension ranging from 600 to 3000 francs.
However, the historian Craig Taylor states that Cousinot is not the author of this chronicle, attributing to him a polemic treatise defending the Valois monarchy against its English counterpart, titled *Pour ce que Plusieurs (La Loy Salique)*, probably written in 1465 in the context of the meetings between Louis XI and Edward IV.
[11] In 1469 he wrote a poetic text, in verse and in prose, Réponse à Robertet sur le départ de la belle Étiennette.