Born at Amid (Diarbekr) about 505, he was there ordained as a deacon in 529 but in 534 we find him in Palestine, and in 535 he passed to Constantinople. The cause of his leaving Amid was probably either the great plague which broke out there in 534 or the furious persecution directed against the Monophysites by Ephrem, patriarch of Antioch, and Abraham (bishop of Amid c. 520-541).
In Constantinople he seems to have early won the notice of Justinian, one of the main objects of whose policy was the consolidation of Eastern Christianity as a bulwark against the pagan power of Persia. 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 also sent, with the rank of bishop, on a mission for the conversion of such pagans as remained in Asia Minor, 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. 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.
In 546 the emperor entrusted him with the task of rooting out the secret practice of idolatry in Constantinople and its neighborhood. But his fortunes changed soon after the accession of Justin II. About 571 Paul of Asia, the orthodox or Chalcedonian patriarch, began (with the sanction of the emperor) a rigorous persecution of the Monophysite Church leaders, and John was among those who suffered most. He gives us a detailed account of his sufferings in prison, his loss of civil rights, etc., in the third part of his History. The latest events recorded are of the date 585, and the author cannot have lived much longer; but of the circumstances of his death nothing is known.
John's main work was his Ecclesiastical History, which covered more than six centuries, from the time of Julius Caesar to 585. It was composed in three parts, each containing six books. The first part seems to have wholly perished. The second, which extended from Theodosius II to the 6th or 7th year of Justin I, was (as F Nau has proved) reproduced in full or almost in full, in John's own words, in the third part of the Chronicle which was till lately attributed to the patriarch Dionysius Telmaharensis, but is really the work of an unknown compiler. Of this second division of John's History, in which he had probably incorporated the so-called Chronicle of Joshua the Stylite, considerable portions are found in the British Museum manuscripts Add. 14647 and 14650, and these have been published in the second volume of JPN Land's Anecdota Syriaca. But the whole is more completely presented in the Vatican manuscript (Codex Zuquenensis, Var. Syr. 162), which incorporates much of John's chronicle in an autographon dated to the 8th century. (English translation, with notes, by Amir Harrak, The Chronicle of Zuqnin, Parts III and IV [Toronto, 1999].)
The third part of John's history, which is a detailed account of the ecclesiastical events which happened in 571-585, as well as of some earlier occurrences, survives in a fairly complete state in Add. 14640, a British Museum manuscript of the 7th century. It forms a contemporary record of great value to the historian. Its somewhat disordered state, the want of chronological arrangement, and the occasional repetition of accounts of the same events are due, as the author himself informs us (ii. 50), to the work being almost entirely composed during the times of persecution. The same cause may account for the somewhat slovenly Syriac style. The writer claims to have treated his subject impartially, and though written from the narrow point of yiew of one to whom Monophysite "orthodoxy" was all-important, it is evidently a faithful reproduction of events as they occurred. This third part was edited by Zureton (Oxford, 1853), and was translated into English by R Payne-Smith (Oxford, 1860) and into German by JM Schonfelder (Munich, 1862).
John's other known work was a series of Biographies of Eastern Saints, compiled about 569. These have been edited by Land in Anecdota Syriaca, ii. 1-288, and translated into Latin by Douwen and Land (Amsterdam, 1889). An interesting estimate of John as an ecclesiastic and author was given by the Abbé Duchesne in a memoir read before the five French Academies on October 25, 1892.