Dionysius was pope from July 22, 259 to December 26, 268. He may have been born in Greece, but this has not been verified. To Dionysius, who was elected pope in 259 after the persecution of Emperor Valerian I, fell the task of reorganizing the Roman church, which had fallen into great disorder. At the protest of some of the faithful at Alexandria, he demanded from the bishop of Alexandria, also called Dionysius, explanations touching his doctrine.

Pope Dionysius sent large sums of money to the churches of Cappadocia, which had been devastated by the marauding Goths, to rebuild and to ransom those held captive. He brought order to the Church and procured a peace after Emperor Gallienus issued the edict of toleration. Dionysius is the first pope who is not listed as a martyr. He died on December 26, 268.

In art, he is portrayed in papal vestments , along with a book.