This article opens up an important but overlooked chapter in the political and diplomatic history of Florence, as well as that of fifteenth-century Franco-Italian relations more broadly. In late 1461, the city of Florence elected ambassadors to go to France to congratulate King Louis XI on his accession to the throne. Intended as a purely ceremonial mission, the Florentine diplomat Piero de' Pazzi ignored his commission and pursued policies that explicitly promoted French interests in Italy. By doing so, Piero sought to improve the standing of his own family, both domestically and abroad, at the expense of the Medici regime in Florence and the anti-French Italian League that the Medici supported. This article offers for the first time a full investigation of a surprisingly early example of tensions between the Medici and the Pazzi, tensions that famously erupted in the Pazzi Conspiracy of 1478.