Saint Dalmatus served in the army of the holy emperor Theodosius the Great (379-395) and attracted his notice. The saint was soon filled with the desire to dedicate himself to his Lord and Creator. Therefore, sometime between the years 381-383, he left the service of an earthly ruler in order to serve the King of Heaven. He went with his son Faustus to Saint Isaac’s monastery near Constantinople in order to speak with him. Saint Isaac (May 30) tonsured both father and son into monasticism, and they both began to lead a strict ascetic life.
Saint Dalmatus excelled all the other monks in virtue. Once, during Great Lent, Saint Dalmatus did not eat any food for the forty days. Later he regained his strength and was found worthy of a divine vision.
The holy ascetic was chosen to be the igumen after the death of the most devout Isaac. In fact, at the Third Ecumenical Council which met in Ephesus in 431 A. D. which condemned the heresy of Nestorius, Saint Dalmatus was honored for his defense of the Orthodox Faith.
After the Council the holy Fathers elevated Saint Dalmatus to be the archimandrite of his monastery, where he died peacefully at the age of ninety (after 446). He was succeeded by his son Faustus, who proved to be a worthy successor of his father.