He pursued studies at the University of Constantinople and eventually became nomophylax of its School of Law.

In 1072, John VIII presided over an assembly of metropolitans and archbishops at the oratory of Saint Alexius in which the question of the election of bishops to vacant sees was discussed.

John, however, recognised that metropolitans sometimes had to remain for a long period in the capital due to ecclesiastical business or illness.

The assembly with John's consent decreed that metropolitans who gave the patriarch advance notification of their intent could again vote while resident in Constantinople.

[5] John VIII has been canonised in the Eastern Orthodox Church and his feast day is celebrated on 30 August.