St. Theophylact (Theophylaktos) was from the East (Asia), and his native city is unknown. He, Theophylaktos lived at Constantinople in the eighth century during the time of the Iconoclast heresy. After the death of the iconoclast emperor Leo IV the Khazar (775-780 AD), Emperor Constantine VI (780-797 AD) ascended the throne. At the same time, the holy Patriarch Paul, not having the strength to continue guiding the flock in the face of iconoclasm, voluntarily resigned his office in 784 AD. St. Tarasios was chosen in his place. At that time, he was an eminent imperial counsellor. Under the supervision of the new Patriarch, the Seventh Ecumenical Council (787) was convened to condemn the Iconoclast heresy. A relatively peaceful time began for the Church, and monasteries again began to fill with monks.
St. Theophylact, a gifted disciple of St Tarasios, with the blessing of the Patriarch, went to a monastery on the coast of the Black Sea with St Michael. God granted the zealous ascetics by their God-pleasing labours and intense prayer the gift of wonderworking. During a drought, when the workers in the field were weakened by thirst, the saints prayed and an empty vessel became filled with enough water to last the entire day.
After several years in the monastery, Patriarch Tarasios consecrated them both as Bishops. St Michael was made Bishop of Synada, and St. Theophylact was made Bishop of Nicomedia.
Heading the Church of Nicomedia, St Theophylact cared for the flock entrusted to him. He built churches, hospices, homes for wanderers; he generously distributed alms, was the guardian of orphans, widows and the sick, and personally attended those afflicted with leprosy, not hesitating to wash their wounds.
When the iconoclast Leo the Armenian (813-820 AD) came to the imperial throne, the terrible heresy burst forth with renewed strength. After the death of St. Tarsios, his successor St. Nicephoros called together a number of Bishops to help him in fighting the iconoclasm of Emperor Leo the Armenian, who reigned from 813-820 AD. Among them was St. Euthymios, Bishop of Sardis, who had attended the holy Seventh Ecumenical Synod (Council) in 787 AD.
St. Euthymios was exiled three times for the sake of the holy icons, and for defying the Emperor Theophilos' command to renounce the veneration of the icons, was scourged from head to foot until his whole body was one great wound, from which he died eight days later, about the year 830.
St. Joseph of Thessalonica, St Michael of Synnada, St. Emilian, Bishop of Cyzicus, also defied the Emperor, with St. Theophylact, who boldly rebuked Leo to his face, telling him that because he despised the long-suffering of God, utter destruction was about to overtake him, and there would be none to deliver him. Leo the Armenian, according to the Saint's prophecy, was slain in church on the eve of our Lord's Nativity, in 820 AD.
For his bold prophecy, St. Theophylact was sent into exile to the fortress Strobilus (in Asia Minor), where he languished for 30 years until his death around 845 AD.
After the restoration of icon-veneration in the year 847 AD under the empress St. Theodora and her son Michael, the holy relics of St. Theophylact were returned to Nicomedia.