He began his military career in the service of Braccio da Montone, who at that time was waging war against Perugia on his own account, and at the death of his chief, shortly followed by that of the latter's son Oddo, Piccinino became leader of Braccio's "condotta".
Alla morte del suo condottiero, avvenuta durante l'assedio dell'Aquila (1424), subito seguita da quella del figlio di quest'ultimo, Oddo Fortebracci, Piccinino divenne la guida della "condotta" di Braccio.