'''Demophilus''' was the Bishop of Constantinople from 370 to 380. He was member of the Homoian [[Arianism|Arian]] faction and thus a [[heretic]].
Little of Demophilus' early life is known. He was born in Thessalonica and was [[Bishop]] of Berea before being elected Bishop of Constantinople in 370 by the Arian party of bishops. Earlier, the Orthodox party in the religiously divided city elected [[Evagrius]] as their bishop, but he and Eustathius, who had consecrated Evagrius to the Constantinople [[see]], were both banished by Emperor Valens, a supporter of Demophilus and the Arian cause. The followers of Evagrius and Eustathius were persecuted severely.
After his ascension as [[patriarch]], Demophilus was unsuccessful in obtaining the election of an Arian as bishop of Cyzicus, a position left vacant after Eucomius was banished. The people of Cyzicus refused to recognize Demophilus, as well as Dorothesus who accompanied him, until after they had [[anathema|anathematized]] [[Aetius of Antioch|Aetius]], [[Eucomius]], and their followers. Demophilus was then allowed by the people to [[consecration of a bishop|consecrate]] a bishop chosen by them. After his consecration the new bishop of Cyzicus taught forthrightly the faith of the [[Nicene-Constantinopolitan Creed|Nicene Creed]].