Eudoxius was one of the most important leaders of the heresy of Arianism during the 4th century. He was from Arabissos of Asia Minor. Against the canons, he took over the see of Antioch after the death of the arian Leontius. The emperor Constantius confirmed his election.
After the Synod of Ancara in 358, Constantius became in favour of the half-arian Basil, bishop of Ancara; and Eudoxius was forced to resort in Armenia. The emperor, however, returned and became in favour of the arian Acacius of Caesaria. At the arians' advice, the emperor selected Eudoxius to become Patriarch of Constantinople.
As Patriarch Eudoxius led the opening ceremony of St Sophia. During the reign of Valens, whom Eudoxius had baptised before his attack against the Goths and has led into Arianism, he fought the Orthodox and managed to expel their bishops, who had returned at the reign of Julian the Apostate.