First intended for a business career, Piero's diplomatic abilities were recognized by Lorenzo de' Medici, who sent him as ambassador to various courts, where he acquitted himself with distinction.
Capponi was then made chief of the republic and conducted public affairs with great skill, notably in the difficult negotiations with Charles VIII of France, who had invaded Italy in 1494 and in whose camp the exiled Medici had taken refuge.
In November 1494 on his way to Naples from Milan, Charles and his large army passed through Lucca into Tuscan territory, occupying Pisa, a city still restless after the Florentine subjugation in 1406.
The Republican Signoria was anxious to be on good terms with him, but he began to imply he would mediate the relationship of France to Pisa and the future role of the deposed Piero de' Medici in Florence.
The temper of the city soon changed, and the citizens began to prepare for the possibility of an urban war with French soldiers already billeted inside the walls.