pope, or antipope, from 963 to 965. The legitimacy of his election has long been debated.

A Roman synod in December 963 deposed and expelled Pope John XII for dishonourable conduct and for instigating an armed conspiracy against the Holy Roman emperor Otto I the Great. Otto, who had marched into Rome with his army and had called the synod, subsequently influenced the election of Leo, then only a layman.

When Otto departed, John and his partisans returned to Rome, where in February 964 John conducted a synod that deposed Leo, who then fled to Otto. John died suddenly in the following May. Ignoring Otto's candidate, Leo, the Romans elected Benedict V. The furious Otto again came to Rome, reinstated Leo by force in June 964, and deported Benedict. Some scholars regard Leo as an antipope until after Otto compelled his acceptance. Others consider either Leo or Benedict as antipopes.