Demophilus was the Bishop of Constantinople from 370 to 380. He was member of the Homoian 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.