In 1587, Ferdinando de' Medici succeeded his brother as Grand Duke of Tuscany, and in 1588 he brought Cavalieri to Florence as an overseer of artists, craftsmen and musicians.

In May 1589, the festivities for the marriage of Grand Duke Ferdinando to Christina of Lorraine included a performance of Girolamo Bargagli's La pellegrina, with six especially elaborate intermedi.

In addition to his musical activities, he was employed as a diplomat during this time, assisting in papal politics, including buying the votes of key cardinals for the elections of popes Innocent IX and Clement VIII who were expected to favour the Medici.

According to Roman records the piece was produced twice that year at the Oratorio de Filippini adjacent to Santa Maria in Vallicella, and was witnessed by thirty-five cardinals.

In 1600 Cavalieri produced Euridice, one of the first operas, by Jacopo Peri (libretto by Ottavio Rinuccini); this was part of an elaborate set of festivities for the wedding of Henry IV of France and Maria de' Medici.

Unfortunately for Cavalieri, he was not given control of the main event, the production of Il rapimento di Cefalo—his rival Giulio Caccini took over from him—and he left Florence in anger, never to return.

This work, probably the most historically important composition of Cavalieri to survive, consists of alternating speech, strophic songs, recitative-like sections and madrigalian parts; subsequent oratorios often used it as a starting-point.

Most importantly, however, it was an attempt to demonstrate, at musically conservative Rome, that the modern monodic style was consistent with the aims of the Counter-Reformation and could be adapted to a religious as opposed to a secular purpose.