Saint John was born at the end of the eighth century. At a young age he became a disciple of Saint Gregory of Decapolis (November 20) and accepted monastic tonsure from him at a monastery in Thessalonica. Under the guidance of this experienced teacher, Saint John attained great spiritual perfection.
When the emperor Leo the Armenian (813-820) renewed the persecution against Orthodox Christians because they venerated the holy icons, Saint Gregory of Decapolis and Saint Joseph the Hymnographer (April 4) and his disciple Saint John went from Thessalonica to Constantinople, to raise opposition to the Iconoclast heresy.
In spite of persecution, Saints Gregory and John fearlessly defended Orthodoxy for several years, and preached the veneration of icons. After many hardships Saint Gregory died (around 820), and soon after, his faithful disciple John also departed to the Lord. Saint Joseph the Hymnographer transferred the relics of Saints Gregory and John and placed them in the church of Saint Nicholas the Wonderworker.