He was one of the bishops summoned by the Patriarch Nikephoros to defend the veneration of the holy icons against the Emperor Leo the Armenian. For this reason he was sent into exile around 815, and after many sufferings for his faithful confession, reposed in exile in 820.
He was a widowed farmer who, though poor, shared the produce of his farm freely with the needy. Once he found some thieves stealing his grain. Without saying who he was, he helped the thieves fill their sacks and make their escape. His virtue became known, and he was ordained to the priesthood, then consecrated bishop. In his own lifetime he was known as a great wonderworker. He reposed in peace.
One of the great ascetics, hesychasts and spiritual teachers of the Church, he did much to restore the knowledge and practice of Orthodox hesychasm. He became a monk at Mt Sinai. He traveled to Mt Athos to learn more of Orthodox spiritual prayer and contemplation, but found that these were almost lost even on the Holy Mountain. The only true, holy hesychast he found there was St Maximos of Kapsokalyvia (Maximos the hut-burner, January 13). Maximos lived a life of reclusion in crude shelters; from time to time he would burn his hut and move to a new one, so as not to become attached even to that poor earthly dwelling. For this, he was scorned as a madman by the other monks. St Gregory upbraided the monks and told them that Maximos was the only true hesychast among them, thus beginning a reform of spiritual life on the Holy Mountain. He spent time teaching mental prayer in all the monasteries of Mt Athos, then traveled around Macedonia, establishing new monasteries. Some of his writings on prayer and asceticism can be found in the Philokalia. He reposed in peace in 1346.