He was a nobleman born in Constantinople, and distinguished himself in a secular career, rising in the year 780 to the rank of protasecretis, Principal Secretary of State to the Emperor Constantine VI and his mother the Empress Irene, who was serving as regent.

His life took a sudden turn when, in 784, Patriarch Paul IV resigned, recommending Tarasios as the only man capable of restoring the Patriarchate, ravaged by the iconoclast heresy, to true Faith and full communion with the other Patriarchates. Tarasios, though unwilling, was virtually forced to accept the Patriarchate by the rulers and the Senate: he agreed at last on condition that an Ecumenical Council be summoned immediately to put an end to the iconoclast heresy. In a few days he was raised from a layman through all the degrees of the clergy and on December 25 784, was consecrated Archbishop of Constantinople.

At Saint Tarasios' insistence, the Imperial rulers summoned a Church Council, whch met at Constantinople in 786. Before its sessions had even begun, iconoclasts burst into the church and drove out the Fathers, who were forced to reconvene in Nicaea, where the first session opened. Patriarch Tarasios presided, and the Council concluded with a condemnation of the iconoclast heresy and the restoration of veneration of the holy images.

As Archbishop, the Saint was a model of humility, compassion, and firmness in the Faith. He refused to have any servants and dressed simply, a living rebuke to the luxury that had corrupted the clergy at that time. His works of charity were so great that he became known to the people as 'the new Joseph': he founded hospices and shelters, distributed the Church's wealth freely to the poor, and often invited the poor to his own table to share his simple fare. He insisted on exercising all gentleness and mercy in restoring repentant heretics to the Church, a policy that met with opposition from the more severe leaders of the Studion monastery. At the same time he was unbending in the defense of the Faith: when the Emperor Constantine came of age he repudiated his wife Mary in order to marry Theodota, one of her servants. The Patriarch refused to bless the adulterous union and threatened the Emperor with excommunication if he persisted in sin. The Emperor had Tarasios imprisoned, forced his licit wife to enter a monastery, and found a priest, Joseph, to bless his second marriage. The following year Constantine was blinded and dethroned, and Tarasios regained his freedom.

The holy Patriarch continued to serve his Church faithfully, occupying the episcopal throne for a total of twenty-six years. In his last years, despite a long and painful illness, he continued to serve the Divine Liturgy daily, supporting himself with his staff. In the year 806, serving at the altar, he began to chant from Psalm 85, Bow down thine ear, O Lord, and hear me, and gave up his soul to God.

"In 820, the Emperor Leo the Armenian, who for seven years had supported the iconoclasts and had fiercely persecuted the Orthodox, had a disturbing dream. He saw a stern-looking Saint Tarasius ordering a man by the name of Michael to run Leo himself through with a sword. Six days later, Leo was in fact assasinated by Michael the Stammerer, who seized power... In physical appearance, Saint Tarasius is said to have closely resembled Saint Gregory the Theologian." (Synaxarion)