Before becoming Pope, he served as Bishop of Caere, which made his election controversial, because, at this stage of history, a bishop was expected never to leave office to move to another see. On three separate occasions he had been employed by the three popes who preceded him as legate to Constantinople, his mission in each case having reference to the controversy excited by Photius, Patriarch of Constantinople.
Among his first acts as pope were the restitution of Formosus as Cardinal Bishop of Portus and the anathematizing of Photius. Due to his respect for King Alfred he freed the Anglo-Saxons of Rome from tribute and taxation. He died in May or June 884, his successor being Adrian III.