Proclus was renowned for the sanctity of his life and for his modesty, with which he succeeded to calm down the Church and to make many Nestorians return to her. Before ascending the throne of Constantinople, he was ordained Bishop of Kyzikos (426-434) by the patriarch Sisinios of Constantinople.
After the death of patriarch Maximian, he was consecrated Patriarch of Constantinople, serving from this rôle for 12 years and 3 months «in a good way» according to the sources. Proclus returned the relics of his teacher St John Chrysostom to Constantinople in 438. He was reknowned for his preaching, for which the Roman officer Valusian (before being baptised a Christian) declared that «if Rome had three men like Sir Proclus, ther would not be there a single pagan.»
With the Tomus to the Armenians, he proves that the basis for the Nestorian heresy are the christological opinons of Theodore Mopsouestias without, however, mentioning him explicitly (435). Speeches and letters of Proclus are saved, and have been published by K. J. P. Migne, F. Schwartz, F. J. Lorey.
To Proclus has wrongly been attributed the «Speech regarding the tradition of Divine Liturgy», which was composed in the 16th century due to the disputes between the Latins and the Protestants regarding the origin of the Divine Liturgy.
Being declared a Saint of the Orthodox Church, his holy memory is honoured on the 20th of November.