Peter was born in Ravenna, Italy, around 1007, the youngest of a large noble, but poor family. Orphaned young, Peter was sent to live with a brother who mistreated him and forced him to work as a swine-herd. A pious boy, Peter was eventually sent to live with another brother, Damian, a priest in Ravenna, Italy; He was known for his life of strict austerity.
Around 1035, Peter gave up teaching to retire from the world and become a Benedictine monk. His health suffered, especially when he tried to replace sleep with prayer. He was forced to spend time in recovery; he used it to study Scripture, and when he was healthy, he was assigned to teach his brother monks and then the public. Economus of Fonte-Avellana; prior of the house in 1043, a post in which he served for the rest of his life. He expanded the monastery, greatly improved its library, and founded sister hermitages in San Severino, Gamugno, Acerata, Murciana, San Salvatore, Sitria, and Ocri. Friend of the future Pope Saint Gregory VII.
Attended a synod in Rome in 1047, and encouraged Pope Gregory VI to support a revitalization of Church zeal and clerical discipline. Wrote Liber Gomorrhianus, which described the vices of priests, mainly in their concern with worldly matters, with money, and the evil of simony. Created cardinal–bishop of Ostia on 30 November 1057. Fought simony. Tried to restore primitive discipline among priests and religious who were becoming more and more worldly. Strongly opposed anti-pope Benedict X. Legate to Milan for Pope Nicholas II in 1059; worked there with Saint Ariald the Deacon and Saint Anselm of Lucca. Supported Pope Alexander II.
A prolific correspondent, he also wrote dozens of sermons, seven biographies (including a one of Saint Romuald), and poetry, including some of the best Latin of the time. He tried to retire to live as a simple monk, but was routinely recalled as papal legate, called upon to make peace between arguing monastic houses, clergymen, and government officials, etc. Declared a Doctor of the Church in 1828.