Baring-Gould’s sources: French Martyrologies. Authority:—A life by an anonymous author of uncertain date, but apparently trustworthy.

S. Severus was the child of very poor Christian parents, who hired him to a nobleman named Corbecan, a heathen, who employed him in tending his herd of mares. The boy loved to pasture the horses in the neighbourhood of a little church dedicated to S. Martin [St. Martin of Tours (d. 397), soldier turned bishop], on the excuse that the herbage there was richer than elsewhere, but really out of love for the House of God. Unable to bear the sight of the misery of the poor, during a cold winter, the boy gave them the clothes off his back, and returned one day through the snow to his master's castle, stripped of everything save his breeches. Corbecan, in a rage, drove him out of the house, and forbade him to shelter in it that night. The lad went to the horses, and crouched among them, taking warmth from their breath. His gentleness and piety, in the end, produced such an impression on Corbecan, that he placed himself under instruction in the faith, and was baptized, he and his whole house. Severus afterwards retired into a solitary place, and lived as an hermit, till a number of disciples gathering round him, he was ordained priest. Against his will he was dragged from his beloved retreat to be consecrated bishop of Avranches. He ruled that see for several years with great zeal and discretion, till the burden became intolerable, and he besought the people to elect a successor. Then he laid down his staff, and retired once more to his forest cell, where he became the master of the blessed Giles. The day of his death is uncertain. His body was translated to the cathedral of Rouen.

In art he is represented with the mares of his master.