Details about his life are known mainly from his first biographer, who, according to some scholars, is the Byzantine philosopher and Ecumenical Patriarch of Constantinople, Gennadius Scholarius.

His mother Theodora was a daughter of the emperor Andronikos II Palaiologos and his father Andrew was the governor of the Peloponnese.

Later, he realized that he should go to north Peloponnese to a specific area close to the modern city of Aigio, in the Achaea region.

On arriving close to Klokos Mountain, he built a small church dedicated to the holy Archangels, and he lived in an inaccessible place, continuing his ascetic life.

Today, the Honorable Body of Saint Leontios is kept in a special shrine in the church of the Holy Archangels inside the monastery.