pope from 254 to 257; he was a priest when consecrated, probably on May 12, 254, as the successor to Pope St. Lucius. Details of Stephen's papacy are known principally through three reports contained in the letters of his rival, Bishop St. Cyprian (Cyprian, Saint) of Carthage.

Stephen I restored the two Spanish bishops Martial of Mérida and Basilides of León-Astorga, whose colleagues accused them of having apostatized by sacrificing to pagan gods during the persecution of Christians under the Roman emperor Decius. The Spanish episcopate, however, did not accept Stephen's restorations and appealed to the African bishops led by Cyprian, who cautioned the Spanish Church against the bishops' reinstatement. Concurrently, the Gallic bishops denounced Bishop Marcianus of Arles as a schismatic follower of Antipope Novatian. Despite a letter from Cyprian endorsing the Gallic position and asking for a successor to the see of Arles, Stephen apparently refused to depose Marcianus.

The third conflict with Cyprian was the most serious. Stephen threatened to excommunicate bishops in Africa (including Cyprian) and in Asia Minor unless they discontinued the practice of rebaptizing heretics. Cyprian composed a defensive treatise that was given support by the Council of Carthage in 256; he vehemently attacked Stephen and dispatched envoys to Rome, threatening a schism between Carthage and Rome. Against Cyprian's argument that each bishop controlled his own see, Stephen staunchly asserted papal supremacy, and he regarded Cyprian's envoys as heretics. At that time the Roman emperor Valerian began his persecution of the Christians, during which Stephen died. It is doubtful, however, that he was martyred.