Helier (in Latin: Helerius) was born in Tongres in Belgium, probably between 510 and 520 AD. He probably arrived in Jersey around 535 - 545 AD. He was martyred in approximately 550-560 AD.
In the 'Acta Sanctorum' published in Antwerp in 1725, the Bollandist Fathers published hagiographies of Helier and his associates. According to the Life of St. Marculf (probably written before 640 AD), Helier's original name was either Eletus or Helibertus.
The Life of St. Helier gives the following information:
Helier's father was a noble of Tongres, called Sigebert (or Sigebard) who married a Swabian woman called Lusegard (or Lusigard). After seven years of marriage, however, they had had no children. They were pagans, but after all prayers to the idols had failed, they turned to a Christian teacher named Cunibert. He agreed to intercede, but made them promise that they would dedicate the child to God as a Christian. Cunibert's prayers were successful, and Sigebert and Lusegard had a son.
However, they immediately reverted to their pagan ways, and forgot their promise. When the boy was seven years old, though, he fell ill and was paralyzed. In desperation, Sigebert finally handed his son over to St. Cunibert, and the boy was cured. Cunibert renamed him Helier and took him into the church and educated him. Helier started performing miracles (among them: negotiating with the rabbits that plagued his garden so that they could share the vegetables that grew there; curing blindness; removing a snake from the mouth of a man who had had the misfortune of having it slither in there while he was asleep). Sigebert was furious because he wanted his son back, and had grave suspicions of the miracles which he ascribed to wizardry, and so he had St. Cunibert killed.
Helier was heartbroken, and ran away. After much wandering (punctuated by more miracles), he was directed by God to go to Nanteuil in the Cotentin, and find a holy man called Marculf. Marculf baptized him and sent him to an island called Gersut, or Agna (i.e. Jersey). There were only about thirty people left on the Island at that time due to regular attacks by Viking pirates. Helier found a little rock to live on by an Islet out in a bay on the South coast and started life as a hermit, attended by a companion called Romard. He was visited by St. Marculf, and while Marculf was there, the Vikings arrived on a raid. Marculf and Helier prayed and made the sign of the Cross, and God raised a mighty storm which destroyed the Vikings and their ships.
Marculf left Helier alone on his rock, and Helier remained there for fifteen years, only eating once a week, until he was so weakened from hunger and the rigors of life on his exposed rock that he could barely move. Eventually Christ appeared to Helier and told him he was to come to Him. Helier said his farewells and prepared himself for martyrdom. Three days later, a large number of Vandals arrived in a fleet of ships and started to lay waste to the Island. One of the Vandals found St. Helier and cut off his head. The Saint picked up his head and walked towards the shore. The Vandals ran away in great terror, and the Island was saved.
St. Helier's body was taken to France, and relics were dispersed to different churches and monasteries. The Islet and the rock on which Helier lived is linked to the mainland of Jersey by a causeway which is walkable at low tide, but covered at high tide. The legend is that the causeway marks the route walked by St. Helier when he carried his head. A small town grew up on the coast and took its name from the saint who was attributed with the conversion of Jersey to Christianity.