He inherited great wealth, but resolved to devote his riches and his talents to the service of the church.
In association with Diodore, afterwards bishop of Tarsus, he supported the orthodox Faith against the Arian heretic Leontius, who had succeeded Eustathius as Patriarch of Antioch.
After the death of Evagrius, (c. 393) Flavian succeeded in preventing the election of a successor, though the Eustathians still continued to hold separate meetings.
Through the intervention of John Chrysostom soon after his elevation to the patriarchate of Constantinople in 398, and the influence of the emperor Theodosius I, Flavian was acknowledged in 399 as the sole legitimate bishop of Antioch.
[1][2] Nevertheless, the Eustathian schism was not finally healed until 415 due to the reconciliation efforts of Alexander (appointed bishop 412), successor to Porphyrios (also spelled Porphyrus).