Jean took part in the Seventh Crusade to Egypt where he was then taken prisoner by Muslims along with the King. When Jean and the King were liberated in May of 1250, they both traveled to Acre, which provided the experiences necessary for Jean's likely authorship of the Chanson d'Acre. During their experiences together, the King and Jean formed a bond which led to Louis appointing Jean to command over fifty of his knights.
After returning to France in 1254, Jean settled into a life of participation in the royal court and estate management. When Louis IX encouraged Jean to take part in the Eighth Crusade, Jean refused and expressed his disapproval of the effort. Jean was concerned for Louis IX, who was physically very weak at the time of the planning of the Eighth Crusade.
Additionally, Jean was concerned for the state of his Kingdom in the King's absence. After the death of Louis, Jean was one of the witnesses heard in the King's canonization inquiry leading to Pope Boniface VIII proclaiming Louis a Saint in 1297. During this period, Jean erected an altar to the Saint in his chapel at St. Laurent at Joinville. Jean finally died at Joinville in 1317.
Jean's Memoir of St. Louis was written after the King's death between 1304 and 1309 for the instruction of Louis X. The source provides especially valuable information on the life of Louis IX, the Seventh Crusade, as well as France in the thirteenth-century.