The Monk John was born at the end of the eighth century. At a young age he became a disciple of the Monk Gregory the Decapolite (+c. 820) and accepted monastic tonsure from him at the Soluneia (Thessalonika) monastery. Under the guidance of this experienced teacher, the Monk John attained to high spiritual accomplishment.

When the emperor Leo the Armenian (813-820) renewed the persecution against Orthodox Christians because of their veneration of holy icons, the Monk Gregory the Decapolite together with the Monk Joseph the Hymnographer (+c. 863) and his student the Monk John set off from Soluneia to Constantinople, to muster opposition to the Iconoclast heresy. In spite of persecution, for several years Saints Gregory and John fearlessly defended Orthodoxy, and preached veneration of holy icons. After many hardships the Monk Gregory died (in about the year 820), and soon after him his faithful student John also expired to the Lord. The Monk Joseph the Hymnographer transferred the relics of Saints Gregory and John and placed them in a church of Saint Nicholas the Wonderworker.