John of Ephesus (or of Asia) (c. 507 – c. 588) was a leader of the non-Chalcedonian Syriac-speaking Church in the sixth century, and one of the earliest and most important of historians who wrote in Syriac.
Born at Amida (modern Diyarbakır in southern Turkey) about 507, he was there ordained as a deacon in 529 by John of Tella at Zuqnin Monastery, but in 534 we find him in Palestine, and in 535 he passed to Constantinople. The cause of his leaving Amida might have been the great plague which broke out there in 542. However he also had already been traveling the region before in order to collect stories for his collection of saints lives. He was back in Amida at the start of the furious persecution directed against the Monophysites by Ephrem, patriarch of Antioch, and Abraham (bishop of Amida c. 520-541). Around 540 he returned to Constantinople and made it his residence.
In Constantinople he seems to have early won the notice of Justinian I, one of the main objects of whose policy was the consolidation of Eastern Christianity as a bulwark against the Zoroastrian power of Persia, through persecution of all the remaining pagans of the empire. John is said by Barhebraeus (Chron. eccl. i. 195) to have succeeded Anthimus as Monophysite bishop of Constantinople, but this is probably a mistake. In any case, he enjoyed the emperor's favor until the death of the latter in 565 and (as he himself tells us) was entrusted with the administration of the entire revenues of the Monophysite Church.
He was sent by Justinian on a mission for the conversion of such pagans as remained in Asia Minor in 542, and informs us that the number of those whom he baptized amounted to 70,000. He also built a large monastery at Tralles on the hills skirting the valley of the Meander, and more than 90 other monasteries, mostly on top of demolished pagan temples. Of the mission to the Nubians which he promoted, though he did not himself visit their country, an interesting account is given in the 4th book of the 3rd part of his History. He was ordained bishop of Ephesus (Asia) for the anti-Chalcedonians in 558 by Jacob Baradaeus.