He began in the service of the Latin emperor Baldwin II, before joining Louis IX of France on the Seventh Crusade.
In July at Chambéry, having settled all his outstanding debts, Baldwin received a new loan from John for 3,433 livres.
[5] John subsequently served King Louis IX of France as a royal sergeant during the Seventh Crusade.
[7] John of Joinville describes the first negotiations thus: He demanded that the emirs make amends for the insults and injuries they had inflicted on the king.
[15] John's activity as lord of Haifa and one of the most important barons of the kingdom of Jerusalem can be traced in documents until the mid-1260s.
Their mission was successful in convincing Urban to levy a hundredth for three years for the defence of the Holy Land.
His goal was to persuade Simon de Montfort to accept the Mise of Amiens and King Henry III to stop appointing foreigners to important offices.
[22] In October 1266, when Louis IX decided to embark a new crusade (the Eighth), he sent John and the archdeacon of Paris to inform Pope Clement IV.
[23] In 1267, Louis sent John with two others to his the court of his brother, King Charles I of Sicily to persuade him to join the expedition or at least provide money.