He studied with Fago at the Conservatorio S Maria della Pietà del Turchini and his first known major performance was of a sacred drama S Chiara or L’infedeltà abbattuta in 1712 at the conservatory.

This work must have found favour with the rulers of Naples for shortly after this he was appointed assistant organist at the vice-regal chapel.

Leo’s 1st opera in 1714 Il Pisistrato was received with acclaim as was his 1718 2nd opera Sfonisba and from 1720 until his death he received a continuous stream of commissions for operas in Naples, Rome, Venice, Bolgna, Turin and Milan

A notable contribution to the genre was the 1723 commedia musicale La’mpeca scoperta. This was to prove a genre in which Leo could flourish in Naples, his serious Neapolitan operas being overshadowed by his rivals Vinci and Hasse despite successes in other Italian cities.

Leo was also a prominent teacher and held positions at the Conservatorio S Maria della Pietà del Turchini (vicemaestro), the Conservatorio S Onofrio (where he succeeded Feo as primo maestro) and finally succeeding his old teacher Nicola Fago at the Conservatorio S Maria della Pietà del Turchini.

One of his greatest contributions to musical development at this time was an attempt to reform religious music in Naples - his 8 part Miserere is an excellent example of this as are the oratorios S Elena al Calvario and La morte di Abele to texts by Metastasio.

In fact there was a great deal of rivalry between Leo and the other great Neapolitan composer of church music at the time Francesco Durante, the city dividing into Leisti and Durantisti.

He became principal organist of the vice-regal chapel on Alessandro Scarlatti’s death in 1725 and succeeded Vinci at the royal chapel in 1730, becoming vice-maestro there in 1737 and maestro di cappella shortly before his death.