He was the son of Arthur II, Duke of Brittany, and his first wife Marie, Viscountess of Limoges.

[1] John was strongly opposed to his father's second marriage to Yolande and attempted to contest its legality.

He was unwilling to cede the Duchy of Brittany to his half-brother John of Montfort, son of his hated step-mother Yolande.

He wished to leave the duchy to the French King Philip VI, but his nobles objected.

After his death, John of Montfort claimed his rights as duke of Brittany, but King Philip VI supported the Blois faction, and the Breton War of Succession (1341–1364) was triggered.