Service at Hagia Sophia
Before his elevation, Theodore served among the clergy of the Great Church of Hagia Sophia. The sources name him keeper of its sacred vessels, the office of skeuophylax, the cleric charged with the custody and protection of the liturgical vessels and treasures of the cathedral. Greek tradition also records that he held the office of synkellos, a close adviser to the patriarch who was frequently regarded as a designated successor.
From this position within the patriarchal household he was chosen to succeed to the throne of Constantinople itself. The synaxaria relate that he was prevailed upon to accept the office rather than seeking it, being constrained by the emperor and the synod to take up the patriarchate after the death of his predecessor.