On 4 February 362, Julian promulgated an edict to guarantee freedom of religion. This edict proclaimed that all the religions were equal before the law, and that the Roman Empire had to return to its original religious eclecticism, according to which the Roman State did not impose any religion on its provinces. Christian chroniclers considered that it had as its purpose the restoration of paganism at the expense of Christianity. Catholic tradition states that Julian also persecuted individual Christians, and that Donatus’ parents, as well as his teacher Pymenius, would die during these persecutions. Donatus escaped to Arezzo and would work with a monk named Hilarian to preach the Christian faith, as well as perform penances and miracles. Severinus' Passio states that Donatus brought back to life a woman named Euphrosina; fought and slew a dragon who had poisoned the local well; gave sight back to a blind woman named Syriana; and exorcised a demon that had been tormenting Asterius, the son of the Roman prefect of Arezzo.
Donatus was ordained a deacon and priest by Saint Satyrus of Arezzo, bishop of that city, and continued to preach in the city and in the surrounding region. At the death of Satyrus, Donatus was appointed a bishop by Pope Julius I. A man named Anthimus was Donatus' deacon.
During a celebration of Mass, at the moment of the giving of Communion, in which a glass chalice was being administered, some pagans entered the church and shattered the chalice in question. Donatus, after intense prayer, collected all of the fragments and joined them together. There was a piece missing from the bottom of the cup; miraculously, however, nothing spilled from the cup. Astounded, seventy-nine pagans converted to Christianity. A similar legend is told of Saint Nonnosus, but the object is a shattered glass lamp.
A month after this episode, the prefect of Arezzo, Quadratian, arrested Hilarian the Monk and Donatus. Hilarian was martyred on July 16, 362 and Donatus was beheaded on August 7 at Arezzo.