John I 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 St. 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 St. 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.