A Roman of upper-class origin, son of the notary Christopher, he was cardinal priest of Sta Susanna and already an old man when he succeeded John X, recently deposed and still alive in prison. He owed his election to Marozia, now head of the house of Theophylact (d. c.920) and, with the titles ‘senatrix’ and ‘patricia’, all-powerful ruler of Rome along with her second husband Guido, marquis of Tuscany. Like his successor Stephen VII, he was a stopgap appointment pending the time when Marozia's own son John was ready to succeed. Virtually nothing is known of Leo's short reign, his only surviving letter being one to the bishops of Dalmatia and Croatia requesting them to be obedient to their archbishop, John of Spalato, to whom he had granted the pallium, and to be content with their territorial boundaries. It is likely, however, that he was entirely dependent on Marozia and the governing clique in Rome. He died well before his hapless predecessor was murdered in prison.
LP ii. 242JW i. 453Z2: 66, 77DBI lxiv. 503–4 (A. Piazzoni)EThC 86 (S. Scholz)Levillain ii. 922 (H. Zimmermann)Watterich i. 33