From a very noble Roman family, descended from the Orsini and therefore related to the Florentine Grand Ducal family, he was one of the most important figures in the cultural and musical life of his time. After the phase of his Roman education, favoured by his father, who was a friend of Michelangelo Buonarroti, he devoted himself to musical studies which saw him actively engaged in the construction of musical instruments and the improvement of the artistic quality of music in Rome since the late 70s. His Florentine story began in the late 1580s when Grand Duke Ferdinand, who had appreciated him during his stay as a cardinal in Rome, called him to Tuscany to make him a point of reference in his programme of development of the arts in the Grand Duchy. Appointed supervisor of all artists, craftsmen and musicians from September 1588 he was housed in Palazzo Pitti with a salary higher than that of the secretaries of state. In addition to directing organ builders and various artists of the Florentine court, he was also very active in the technical field and inventions. One of the first and important tasks of the Florentine years was the organization, as superintendent, of the entire cycle of celebrations for the wedding of Ferdinand to Christine of Lorraine and in particular for the intermedi of La Pellegrina. His role is historicized in a Grand Duke’s declaration that tends to recognize him as the highest rank in the hierarchy of the organizers of the festivities: “having the Grand Duke at present at his service Emilio de’ Cavalieri gentilhuomo romano, in whose valor he trusted, deputed him ... above the present comedy with full authority”. De’ Cavalieri composed for them the solo with improvised embellishments Godi turba mortale (intermedio VI) on a text by Rinuccini. Even more important was his contribution to the final dance O che nuovo miracolo for which he also designed the choreography.
In it De’ Cavalieri created a perfectly organized musical structure that by unity, logic and extension can be considered unique in its time. With the title of Aria di Fiorenza or Ballo del Granduca the piece spread and influenced countless compositions in the European courts. Probably the de’ Cavalieri who was never part of the Camerata dei Bardi, although he collaborated with the founder Giovanni in the above mentioned intermedi, was also the author of the choirs for the Florentine performance of Aminta. Certainly de’ Cavalieri was the first known composer to adapt the dramatic show to music; his pastoral works defined to some extent the literary genre of the first opera librettos. Returning to Rome for the Holy Year in 1600, he composed his most famous work Rappresentatione di Anima et di Corpo. The booklet represents the first case of music printed with continuous bass in a detailed and accurate manner. Returning to Florence in the same year for the preparations for the wedding of Maria dei Medici to Henry IV of France, he was at least active in the composition of the Contesa di Giunone e Minerva presented during the wedding banquet in Palazzo Vecchio. The interference of the Grand Duke’s brother Don Giovanni de' Medici's embittered the nobleman who, after the end of the celebrations, returned to Rome, not forgetting, however, to point out the responsibility for the relative failure of those celebrations: “and if Signor Don Giovanni had wanted a little opinion from me, about the music of the comedy, and even from Bernardo on the things belonging to the machines, I believe that everything would have been finished and the music would be proportionate to the place and the theatre”. Emilio De’ Cavalieri never returned to Florence and died in Rome in 1602. Although musical historiography attributes to the representation of Euridice by Peri in 1600, the authorship of the new monodic style, Emilio De’ Cavalieri should be recognized as the true animator of the reform, starting from the feasts of 1589.