In 1527, after the Sack of Rome by Imperial Troops, the Medici are chased from Florence. The oligarchic government of the Dieci is reinstated. The Dieci need a new ambassador. In particular, they need a man of trust in France, where the king ought still to be convinced to defend Florence and Tuscany against imperial troops. They choose pro-republic Bishop Giuliano Soderini of Saintes. The embassy and life of Giuliano Soderini have been strangely and almost systematically omitted in the existing literature on the subject. His letters were completely excluded from previous editions of Florentine letters of this period. This paper aims to restore them to their rightful place. It presents Giuliano Soderini’s personal and political background before and after his French mission. His diplomatic functions, needs and difficulties are detailed thanks to an extended and thorough reading of his correspondence in and out of France, preserved in France and Italy. This archival work led to the writing of an updated catalogue of his diplomatic correspondence from July 1527 to February 1529.