He was a descendant of the Orsini family, one of the oldest, most illustrious, and for centuries most powerful of the Roman princely families, whose origins, when stripped of legend, can be traced back to a certain Ursus de Paro, recorded at Rome in 998.

Cast off by his father at the age of nine, he found a refuge among the choir boys of St. John Lateran, and a protector in Canon Gentile Delfini.

He applied himself energetically to the study of the ancient languages, published a new edition of Arnobius and of the Septuagint, and wrote works dealing with the history of Rome.

Fulvio Orsini was a Renaissance genius who combined antiquarianism and philology in his research work.

"His library was developed block by block acquisitions of books belonging to humanists: those of Angelo Colocci (1474-1549), Orsini's former master, Michele Forteguerri († after 1560), Pomponius Laetus (1428-1498), Pietro Bembo (1470-1547), Ange Politien (1454-1494), ...".