Thomas Agni of Leontino, Dominican archbishop of Cosenza, and later patriarch of Jerusalem, was the first to write a life of the blessed martyr. He lived for many years with Peter of Verona and had been his superior.
He was born in the city of Verona into a family perhaps sympathetic to the Cathar heresy. Peter went to a Catholic school, and later to the University of Bologna, where he is said to have maintained his orthodoxy and at the age of fifteen, met Saint Dominic. Peter joined the Order of the Friars Preachers (Dominicans) and became a celebrated preacher throughout northern and central Italy.
From the 1230s on, Peter preached against heresy, and especially Catharism, which had many adherents in thirteenth-century Northern Italy. Pope Gregory IX appointed him General Inquisitor for northern Italy in 1234. and Peter evangelized nearly the whole of Italy, preaching in Rome, Florence, Bologna, Genoa, and Como. In 1243 he recommended the new Servite foundation to the pope for approval.
In 1251, Pope Innocent IV recognized Peter's virtues (severity of life and doctrine, talent for preaching, and zeal for the orthodox Catholic faith), and appointed him Inquisitor in Lombardy. He spent about six months in that office and it is unclear whether he was ever involved in any trials. His one recorded act was a declaration of clemency for those confessing heresy or sympathy to heresy.
In his sermons he denounced heresy and also those Catholics who professed the Faith by words, but acted contrary to it in deeds. Crowds came to meet him and followed him; conversions were numerous, including many Cathars who returned to orthodoxy.