Stephen I succeeded Lucius I as Bishop of Rome on May 12, 254. His three-year pontificate is principally significant for the foundational controversy over the validity of baptism conferred by heretics — the so-called Re-baptism Controversy.
The North African churches led by Cyprian of Carthage (see his entry already in the catalogue) held that baptism conferred by heretics was invalid and must be repeated when heretics or schismatics returned to the Catholic Church. Stephen — relying on a settled Roman tradition that went back centuries — held that baptism conferred by anyone using the proper Trinitarian formula was valid and that the returning heretic needed only the laying on of hands for reconciliation, not re-baptism. The dispute exploded in 256, with Cyprian convening African synods that affirmed the African position and Stephen issuing emphatic Roman letters condemning the practice of re-baptism as innovative and contrary to apostolic tradition.
The dispute reached the brink of formal schism between Rome and Carthage but was overtaken by the Valerian persecution of 257–260, which killed Cyprian (September 14, 258) and almost certainly Stephen himself (August 2, 257). The Roman position was vindicated at the 314 Council of Arles and was definitively established as Catholic doctrine at the Council of Trent — Stephen's foundational stance is one of the most important early Catholic interventions on sacramental theology. He is buried in the Crypt of the Popes at the Catacombs of San Callisto.