Pietro Giovanni Guarneri was the son of Andrea Guarneri and uncle of del Gesł. He was born in 1655 in Cremona and died in 1720. His father was Andrea Guarneri.
He was trained in his father's shop along with his brother Guiseppe who is usually called Filius Andreae (i.e. son of Andrea) or simply Filius and who was the father of Guiseppe del Gesł.
Unlike his brother who stayed in Cremona in Andrea's shop, Pietro left Cremona as a young man to pursue a career in nearby Mantua (about 30 miles) as a violinist.
He was apparently in charge of the music in the ducal court at Mantua (each city was a little kingdom at that time) and spent his life primarily as a musician.
His father was probably not at all happy about this. Nevertheless, he was extremely talented as a violinmaker and continued making a few violins, perhaps at the request of his noble patrons.
It appears he never made any viola or violincello.
Because he lived in Mantua, he is known as Pietro of Mantua or Peter of Mantua. As few as 50 instruments exist by Peter of Mantua.