John of Antioch was bishop of Antioch A.D. 429-441 and led a group of moderate Eastern bishops during the Nestorian controversy. He is sometimes confused with John Chrysostom, who is occasionally also referred to as John of Antioch.
John gave active support to his friend Nestorius in the latter's dispute with Cyril of Alexandria. In the year 431, he arrived too late for the opening meeting of the Council of Ephesus. Cyril, suspecting John of using Fabian tactics to support Nestorius, decided not to wait and convened the council without John and his supporters, condemning Nestorius. When John reached Ephesus a few days after the council had begun, he convened a counter-council which condemned Cyril and vindicated Nestorius.
Two years later, in 433 John reconciled with Cyril based on the Formula of Reunion, a theological formula devised as a compromise. In the process, John lost many of his own supporters within his patriarchate.
Some of his letters are extant.
Source
The Oxford Dictionary of the Christian Church (3rd ed.), p. 887
According to Tillemont, he was born at Antioch in 393, and died either at Cyrrhus ("about a two-days' journey east of Antioch" or eighty Roman miles), or at the monastery near Apamea (54 miles south east of Antioch) about 457.
At a young age he became a lector among the clergy of Antioch, then resided a while in a monastery, was a cleric at Cyrrhus, and in 423 became bishop over a diocese about forty miles square and embracing 800 parishes, but with an insignificant town as its see city.
Theodoret shared in the petition of John I of Antioch to Nestorius to approve of the term theotokos ("mother of God"), and upon the request of John wrote against Cyril's anathemas.