Paul I was the biological brother of his predecessor Pope Stephen II — both born of a Roman aristocratic family, both raised in the Lateran ecclesiastical patronage tradition. He had served as his brother's principal deacon and diplomatic representative during the foundational Franco-papal embassies of 754–756.
Elected on May 29, 757, he continued his brother's foundational Carolingian alliance with King Pippin the Short — maintaining the institutional foundation of the new Papal States during the critical decade of their consolidation.
He was a notable patron of monastic communities in Rome — founding the Greek monastery of San Silvestro in Capite (763) and translating relics of Roman martyrs from the catacombs into the city churches (a foundational shift from the late-antique tradition of extramural martyr-veneration to the medieval urban-church relic-translation tradition). His preservation of catacomb relics rescued countless martyr-remains from the decay of the abandoned cemeteries.
He maintained correspondence with the Byzantine iconoclast emperor Constantine V, vigorously defending the veneration of images — providing the foundational western papal endorsement of icon-veneration that would shape the eventual Catholic resolution of the iconoclast crisis at the Second Council of Nicaea (787). He died on June 28, 767, and was buried in St. Peter's.