[1] Born in Rome, he was appointed bishop of Muro Lucano by Pope Pius IV (Medici) in consistory on 29 November 1560.
On 10 July 1561, Flavio Orsini, Bishop of Muro and Auditor of Causes in the Apostolic Camera, transmitted a motu proprio of Pope Pius IV granting a feudal investiture to Baldassare Rangoni of Modena.
[3] On 3 September 1563, the Bishop of Muro was judge ordinary in the curia, hearing a testamentary dispute from the diocese of Ajaccio.
[5] In his fourth consistory for the creation of cardinals, on 12 March 1565, Pope Pius IV named Flavio Orsini a cardinal-priest, and on 15 May assigned him the titulus of San Giovanni a Porta Latina.
[6] On 19 September 1570, Pope Pius V (Ghislieri) appointed a commission of two cardinals, Giovanni Poliziani and Flavio Orsini, to complete the repairs on the Aqua Vergine and connect various fountains, including the Trevi.