This glorious and wonderworking saint was born in the city of Salonica of well-born and devout parents. Begged of God by these childless parents, Demetrius was their only son and was, because of this, most carefully cherished and educated. His father was the military commander of Salonica, and, when he died, the Emperor made Demetrius commander in his place. In doing this, the Emperor Maximian, an opponent of Christ, particularly recommended him to persecute and exterminate the Christians in Salonica.

Demetrius not only disobeyed the Emperor: he openly confessed and preached Christ the Lord in the city. Hearing of this, the Emperor was furious with Demetrius and, at one time, on his way back from a war against the Sarmathians, went to Salonica especially to look into the matter. The Emperor, therefore, summoned Demetrius and questioned him about his faith. Demetrius proclaimed openly before the Emperor that he was a Christian, and, furthermore, denounced the Emperor's idolatry. The enraged Emperor cast him into prison. Knowing what was awaiting him, Demetrius gave his goods to his faithful servant, Lupus, to give away to the poor, and went off to prison, glad that suffering for Christ was to be his lot.

In the prison, an angel of the Lord appeared to him and said: 'Peace be with thee, thou sufferer for Christ; be brave and strong!' After several days, the Emperor sent soldiers to the prison to kill Demetrius. They came upon the saint of God at prayer, and ran him through with their spears. Christians secretly took his body and gave it burial, and there flowed from it a healing myrrh by which many of the sick were healed. A small church was very soon built over his relics.

An Illyrian nobleman, Leontius, became sick of an incurable illness. He ran prayerfully up to the relics of St Demetrius and was completely healed, and in gratitude built a much larger church in place of the old one. The saint appeared to him on two occasions. When the Emperor Justinian wanted to take the saint's relics from Salonica to Constantinople, a spark of fire leapt from the tomb and a voice was heard: 'Leave them there, and don't touch!', and thus the relics of St. Demetrius have remained for all time in Salonica. As the defender of Salonica, St. Demetrius has many times appeared and saved the city from calamity, and there is no way of counting his miracles. The Russians regarded St. Demetrius as the protector of Siberia, which was overcome and annexed by Russia on October 26, 1581.