Saint Philotheus was a native of Thessalonica, and received the monastic tonsure at an early age. After living for a time at Mt Sinai, he went to Mt Athos and became the igumen of the Great Lavra.
In 1347 he became Metropolitan of Heraclea, Thrace. Later, he served as Patriarch of Constantinople from 1354-1355, and again from 1364-1376.
While living on the Holy Mountain and even after he left there, St Philotheus wrote religious books which reveal his great learning and spirituality. Many of his works are directed against the anti-hesychasts, and he also wrote on liturgical and hagiographical themes.
St Philotheus ordained that St Gregory Palamas (November 14) be commemorated on the second Sunday of Great Lent, presided at his glorification as a saint, and even composed the Service in his honor.
St Philotheus fell asleep in the Lord in 1379.