He was born in Neapolis (Naples) to a pagan father and a Christian mother, and became an officer in the Roman army. Though he was not baptised, his mother had secretly instructed him in the Christian faith. Once, in a battle, his company was completely surrounded by the enemy, and Nikon recalled his mother's counseling that, whenever he was in trouble, he should make the sign of the Cross and call upon Christ. This he did, and was immediately filled with strength and resolution, so that the enemy's army was routed. Nikon went home, openly crying out 'Great is the God of the Christians!' to the great joy of his mother.

He traveled secretly to Cyzicus in Asia, where the bishop Theodosius baptised him. He then entered a monastery to spend his days in prayer and study. But some years later Theodosius, who was near death, had a vision in which he was told to consecrate Nikon as his successor. He summoned Nikon from the monastery and, to the monk's amazement, immediately ordained him a deacon, then a priest, then a bishop.

Later, bishop Nikon returned to Italy to preach the Gospel of Christ. In Naples, he found his mother still alive, and remained with her until her death. He then set out with nine disciples, former fellow-soldiers, to proclaim the Faith. Through the Saint's grace-filled preaching and example, many more disciples were soon added to this number. At that time a great persecution of Christians was underway, and Quintinianus, ruler of that region, seized Nikon and his companions and handed them over to the torturers. One hundred ninety of Nikon's companions perished under torture. Nikon himself was beaten, flayed, and even thrown from a high cliff, but was miraculously preserved. Finally he was slain by the sword and his body thrown in a field to be eaten by the beasts. A shepherd boy, possessed by a spirit of madness, found the body, fell on it, and was instantly healed. He told his story to some Christians, who found the body and gave it honorable burial. Saint Nikon contested during the reign of the Emperor Decius.