John was the eldest son of John I of Brittany and Blanche of Navarre. On 22 January 1260, he married Beatrice, a daughter of King Henry III of England. John was very close to his brother-in-law, the future King Edward I. In 1271, he accompanied Edward to the Ninth Crusade, meeting there with his father and King Louis IX of France. Louis succumbed to an illness in Tunis, and John's father returned to Brittany. John, however, followed Edward to Palestine. The crusade ended the following year, having achieved little. In 1285, John took part in the Aragonese Crusade at the side of King Philip III of France.