He studied at the University of Rome La Sapienza, took his degree in 1855 in natural science and mathematics, and entered his uncle's pharmacy as assistant. His scanty leisure was, however, given to study. He learned Greek by himself, and gained facility in the modern language by conversing with the Greek students at the university. In spite of all disadvantages, he not only mastered the language, but became one of the chief classical scholars of Italy.
In 1857 he published, in the Rheinisches Museum, a translation of some recently discovered fragments of Hypereides, with a dissertation on that orator. This was followed by a notice of the annalist Granius Licinianus, and one on the oration of Hypereides on the Lamian War. In 1859 he was appointed professor of Greek at Pisa on the recommendation of the duke of Sermoneta. A few years later he was called to a similar post at Florence, remaining emeritus professor at Pisa also.
He subsequently took up his residence in Rome as lecturer on Greek antiquities and greatly interested himself in the Roman Forum excavations. He was a member of the governing bodies of the academies of Milan, Venice, Naples and Turin.
The list of his writings is long and varied. Of his works in classical literature, the best known are an edition of the Euxenippus of Hypereides, and monographs on Pindar and Sappho. He also edited the great inscription which contains a collection of the municipal laws of Gortyn in Crete, discovered on the site of the ancient city.
In the Kalewala and the Traditional Poetry of the Finns (English translation by IM Anderton, 1898) he discusses the national epic of Finland and its heroic songs, with a view to solving the problem whether an epic could be composed by the interweaving of such national songs. He comes to a negative conclusion, and applies this reasoning to the Homeric problem. He treats this question again in a treatise on the so-called Peisistratean edition of Homer (La Commissione omerica di Pisistrato, 1881).
His Researches concerning the Book of Sindibad have been translated in the Proceedings of the Folk-Lore Society. His Vergil in the Middle Ages (translated into English by EFM Benecke, 1895) traces the strange vicissitudes by which the great Augustan poet became successively grammatical fetich, Christian prophet and wizard. Together with Alessandro d'Ancona, Comparetti edited a collection of Italian national songs and stories (9 vols, Turin, 1870-1891), many of which had been collected and written down by himself for the first time.
- Sir John Edwin Sandys (1908). A history of classical scholarship ... At the University press. pp. 244–.
- This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press.