A Roman presbyter, he was the Roman militia's candidate for the papacy at the disputed election following the death of John V on 2 Aug. 686. His rival, backed by the clergy, was the archpriest Peter, and in the resulting impasse a compromise candidate, Conon, was proposed, elected, and consecrated. On Conon's death on 21 Sept. 687 there was again a dispute about the succession, two candidates being put forward and elected by separate factions, the archdeacon Paschal and Theodore, who in the meantime had become archpriest. With their partisans they hastened to the Lateran, Theodore arriving first and occupying the inner apartments, and Paschal following and taking over the outer ones. Again resort was had to a compromise candidate, this time Sergius, titular priest of Sta Susanna, who was elected and, his election having been ratified by the Byzantine exarch in Italy, duly consecrated. When Sergius I was installed in the Lateran, Theodore accepted defeat with good grace, came forward, and embraced him in token of submission. Nothing further is known about him, and as he was never consecrated and accepted Sergius as legitimate pontiff, he is doubtfully reckoned an antipope.
JW i. 243 f.LP i. 368, 371 f.Caspar ii. 621 f.Bertolini 396 f.EThC 144 (M. Heim)Levillain iii. 1486 (J. Durliat)Seppelt ii. 80 f.JR 206–8