Pope Leo VIII (c. 915 – 1 March 965) was a Roman prelate who claimed the Holy See from 963 until 964 in opposition to John XII and Benedict V and again from 23 June 964 to his death.

In 963, he was included in a party that John sent to the newly crowned Holy Roman emperor, Otto I, who was besieging the deposed King Berengar II of Italy at the castle of St. Leo in Umbria.

Since Leo was still a layman,[4] he was ordained as ostiarius, lector, acolyte, subdeacon, deacon and priest in the space of a day by Sico, the cardinal-bishop of Ostia, who then proceeded to consecrate him as bishop on 6 December 963.

[11] Then, after having the Roman nobility swear an oath over the Tomb of Saint Peter to obey and be faithful to Leo, Otto departed Rome in late June 964.

In addition, Leo is also claimed to have relinquished to Otto all the territory of the Papal States that had been granted to the Apostolic See by Pepin the Short and Charlemagne.

The Annuario Pontificio makes the following point about the pontificate of Leo VIII: "At this point, as again in the mid-eleventh century, we come across elections in which problems of harmonizing historical criteria and those of theology and canon law make it impossible to decide clearly which side possessed the legitimacy whose factual existence guarantees the unbroken lawful succession of the Successors of Saint Peter.

However, if Benedict did consent to his deposition as Liutprand of Cremona (who chronicled the events of this period) wrote, and if, as seems certain, no further protest was made against Leo's position, it has been the consensus of historians that he may be regarded as a true pope from July 964 to his death in 965.