(16 Apr. 556–3 Mar. 561)
A Roman, nobly born and rich, he was widely experienced and elderly when appointed. As a deacon he had accompanied Agapitus I in 536 to Constantinople, after his death representing the holy see at the anti-monophysite synod held there in May–August. When Silverius was exiled in 537, Pelagius was alleged, in deference to Empress Theodora's wishes, to have worked to prevent his return in order to retain the papacy for Vigilius. He had stayed in Constantinople as Vigilius' apocrisiarius and become the confidant of Emperor Justinian (527–65), who had consulted him on church appointments, used him on delicate missions, and under his influence published (early 543) a denunciation of the Greek theologian Origen (d. c.254). In 544, when Justinian issued his edict condemning the Three Chapters, Pelagius had been in Rome, but had sought theological ammunition against it from Ferrandus of Carthage (d. 546/7). In 546, when Rome was besieged by the Goths, he had played a noteworthy role as vicar of the absent pope, spending lavishly on famine relief and, when the city fell (17 Dec.), intervening with the Gothic king Totila to prevent a massacre. Totila had sent him (547) to Constantinople to negotiate peace, but without success.
For the rest of his diaconate he had been deeply involved with the controversy over the Three Chapters. Like the west generally, he had rejected Vigilius' Iudicatum (547) condemning them. Returning to Constantinople in 551, he had stiffened the vacillating Vigilius' opposition to their condemnation, sharing his ill treatment, backing his demand for a general council to reassure the west, and, when it met in a form unlikely to do so, supporting his refusal to take part. It was he who had drafted Vigilius' First Constitution. When the pope weakened and issued a Second Constitution, he had broken with him and, imprisoned in monasteries, had written, with other pamphlets, a Defence of the Three Chapters, branding Vigilius in it as a turncoat. But now he made an abrupt change of stance, accepting both the condemnation of the Three Chapters and the Fifth General Council. The reasons for his volte-face are obscure. It is likely that he had realized that Vigilius' endorsement of the council created a new situation, but also likely that he was aware that Justinian, who despite differences had never ceased to admire him, wished him to be the next pope provided he fell into line with his religious policy.
On Vigilius' death he returned to Rome as the emperor's nominee for the papacy. There seems to have been no election, but LP suggests that Justinian may have obtained the grudging assent of the Roman clergy in Constantinople. Not surprisingly, Pelagius had a hostile reception, many religious and nobles withdrawing from communion with him. His consecration had to be postponed until 16 Apr. 556 since no bishop would officiate, and it was then carried out by only two bishops (of Perugia and Ferentino), while a presbyter represented the bishop of Ostia, normally a papal consecrator. Rumour implicated him in Vigilius' death, and he was execrated for his betrayal, as the west regarded it, of the Three Chapters. It is significant that, after his ordination, he broke precedent by solemnly affirming his loyalty to the first four general councils, especially Chalcedon (451), and in St Peter's, supported by the governor Narses and holding aloft a cross and the book of the gospels, swore that he had done no harm to Vigilius.