The twenty-second of the See of Saint Mark (380-385). Timothy was unanimously elected to succeed PETER II. An elderly man at the time of his election, Timothy was associated with ATHANASIUS in his earlier years and must have been profoundly influenced by his theology. He is known to have disposed of all his worldly possessions in favor of the church and the poorer folks of his Christian community.

His reign was relatively peaceful, and the major event of his time was the famous Council of CONSTANTINOPLE. The council was summoned in May 381 by I, who was eager to ensure the unity of the church within the empire after the defeat of the Arians, the triumph of Athanasian orthodoxy, and the confirmation of the Nicene Creed. Participants in the council numbered 150 Orthodox bishops and 36 Macedonians, who were regarded as heretics. The Egyptian and his suffragan bishops arrived a little late to find GREGORY OF NAZIANZUS, bishop of Constantinople, and Melitius, bishop of Antioch, presiding over the council, which seems to have irked the Egyptian delegation. However, Melitius died during the meeting and Gregory resigned from his see. The appointment of Nectarius to succeed Gregory as bishop of the capital was ratified by the council.

It would seem that Timothy assumed the presidency of the council in that period. Although Rome was not represented at the council, its decisions were binding to East and West. The Nicene doctrine concerning the divinity and humanity of the person of Jesus was ratified and the of was condemned. The question of the indivisibility of from the Father and the Son was also settled at this council. On the ecclesiastical front, Flavian rather than Paulinus was nominated to succeed Melitius as bishop of Antioch. The problem of ranks was discussed, and the primacy of Rome was confirmed. Henceforth, the bishop of Constantinople came second, the bishop of Alexandria third, the bishop of Antioch fourth, and the bishop of Jerusalem fifth.

Timothy was a great supporter of monastic orders, and he is known to have recorded the lives of eminent monks, now lost and known only through the work of SOZOMEN, who used them as sources. Timothy is also known to have made a number of responses to clerical questions, and his answers became part of the church legal system.