(1 Oct. 965–6 Sept. 972)
A Roman, son of John Episcopus (a surname) but not related, as is often supposed, to the powerful Crescentii, he was brought up in the papal court, held successive offices and was librarian under John XII, and was then promoted bishop of Narnia in Umbria. Five months after Leo VIII's death (in the interval the Romans had vainly asked for the restoration of Benedict V) he was elected pope with the agreement of two bishops, Otger of Spire and Liutprand of Cremona, whom Emperor Otto I (962–73) sent to Rome to represent him. He was a compromise appointment; but if Otto reckoned that he could rule Rome better with an establishment figure as pope, his choice at first seemed disastrous, for John's dependence on a German sovereign combined with his high-handed rule made him hated in the faction-riven city. In Dec. 965 it revolted; John was assaulted, imprisoned in Castel Sant'Angelo, and banished to the Campagna, but he managed to escape, made contact with the emperor, and on 14 Nov. 966, the Romans having repented of their foolhardiness, returned in triumph. Otto reached Rome at Christmas, and the participants in the revolt were punished with gruesome brutality.
From now onwards John was protected by the emperor, who resided in Italy until summer 972. Although John was a mainly subservient partner, the two worked together to their mutual benefit. At a synod at Ravenna in Apr. 967 Otto confirmed the restoration to the papal state of large territories, including the former exarchate, which it had lost. Measures were taken, probably inspired by Otto, to promote clerical celibacy and continue favours to the monastery of Cluny, near Mâcon. For his part John definitively raised Magdeburg to an archbishopric, a project dear to the emperor's heart, agreed by John XII in 962 but hitherto obstructed by the bishops of Mainz and Halberstadt. Otto's original idea had been to make it the base for the conversion of all the Slavs east of the Saale and Elbe, but in his bulls (20 Apr. 967 and 18 Oct. 968) confirming its privileges and granting the pallium to its first archbishop, Adalbert, John limited the see to ‘the recently converted Slavs’ and assigned the creation of new bishoprics not to the emperor but to the metropolitan: evidence, it has been claimed, that he retained some independence.
At Christmas 967 John crowned Otto's 12-year-old son Otto II (955–83) as co-emperor. The urgency, in view of the restoration of the western empire in 962 and of Otto's efforts to extend his control in territories in southern Italy under Byzantine suzerainty, of putting relations with Constantinople on a constructive footing was now obvious. Otto formed the plan of achieving this by a diplomatic marriage, and on 14 Apr. 972 John married Otto II and the Greek princess Theophano, niece of Emperor John I Tzimisces (969–76), and crowned her. Even so, tension between the eastern and western churches could not be avoided; when John, in support of Otto's political designs, erected Capua and Benevento into metropolitan sees, the patriarch of Constantinople retaliated by making the bishop of Otranto an archbishop with five suffragans under him and attempting to check Roman influence in the Byzantine provinces of Apulia and Calabria.