Little is known of Benedict's life before his papacy. He was educated and lived in Rome and was cardinal priest of S. Callisto at the time of his election. Benedict had a reputation for learning and piety. He was elected upon the refusal of Hadrian, the initial choice of clergy and people. A group of important people preferred a different candidate, Anastasius. This latter group had Benedict's election disavowed and Anastasius installed. However, popular opinion was so strong that Benedict's consecration was allowed. The Emperor Louis II's envoys forced Benedict to handle Anastasius and his adherents leniently. The schism helped to weaken the hold of the emperors upon the popes, especially upon their elections.
Benedict intervened in the conflict between the sons of Lothair I (the future Lothair II, Louis II and Charles) on the latter's death. He was active in other cases and adopted a firm position towards Constantinople.