In 1337 he inherited from his grandfather Ebal the fief of Fénis, after a series of disputes with his brother Ebal (who acquired Ussel Castle and Saint-Marcel) and his four uncles.
Around 1340 he started the enlargement of the Fénis Castle, adding the central pentagonal body which is still visible.
Aymon held several military and diplomatic positions for the Duchy of Savoy, such as a castellan of Lanzo, Moriana, Avigliana, Chambéry, Tarentaise, Susa, Montmélian, Ivrea, Bard, Sallanches and Castruzzone, governor of Ivrea and bailiff of Val di Susa and Savoy.
Between 1354 and 1357 he received from Amadeus VI of Savoy the fief of Aymavilles and restored its castle.
His second son Amadeus received Aymavilles, starting the cadet line of the Challant-Aymavilles.