was at a very early age appointed reader in the church at Constantinople. He was also employed as secretary or amanuensis to St. Chrysostom, and was employed in a similar capacity by Atticus (who succeeded Arsacius as patriarch of Constantinople), by whom he was invested successively with the orders of deacon and presbyter. He was raised to the rank of bishop of Cyzicus by Sisinnius, the successor of Atticus, but did not exercise the functions of his office, the people of Cyzicus choosing another in his place. On the death of Sisinnius (A. D. 427) there was a general expression of feeling in favour of Proclus as his successor, but Nestorius was appointed. Proclus contended zealously against the heresies which the latter strove to introduce into the church, combating them even in a sermon preached before Nestorius himself. On the deposition of Nestorins, Proclus was again proposed as his successor; but his elevation was again opposed, though on what grounds does not appear very clearly ascertained. But on the death of Maximianns, who was appointed instead, Proclus was at last created patriarch. In A. D. 438 Proclus gained a great deal of honour by having the body of St. Chrvsostom brought to Constantinople. There is still extant a fragment of a Latin translation of an éloge on St. Chrysostom, by Proclus, delivered probably about this time. It was in the time of Proclus that the custom of chanting the Trisagion was introduced into the church. While in office, Proclus conducted himself with great prudence and mildness. For further details respecting his ecclesiastical career, the reader is referred to Tillemont's Mémoires Ecclésiastigucs (vol. xiv. pp. 704-718). His extant writings are ennmerated by Fabricius (B. G. vol. ix. pp. 505-512). One of the most celebrated of his letters (περὶ πίστεως) was written in A. D. 435, when the bishops of Armenia applied to him for his opinion on certain propositions which had been disseminated in their dioceses, and were attributed to Theodorus of Mopsuestia. The discussion that ensued with respect to these propositions made a considerable stir in the East.

Proclus bestowed a great deal of pains upon his style, which is terse and sententious, but is crowded with antitheses and rhetorical points, and betrays a laboured endeavour to reiterate the same sentiment in every possible variety of form. From the quotations of subsequent authors, it appears that several of the writings of Proclus are lost. The of Proclus Diadochus has sometimes been erroneously described as a theological work of St. Proclus. The 24th of October is the day consecrated to the memory of St. Proclus by the Greek church.