He was descended of a good family in Kent.  From his infancy he turned all his thoughts and affections to attain to the most perfect love of God, and studies to devote all his moments to this glorious pursuit.  In this earnest desire, in the twelfth year of his age, he retired into wilderness, and chose for his dwelling a great hollow oak tree; whence the surname of Stock was given to him.
While he here mortified his flesh with fasting and other severities he nourished his soul with spiritual dainties in continual prayer.  His drink was only water, and he never touched any other food but herbs, roots and wild apples.  While he led his course of life, he was invited by a divine revelation to embrace the rule of certain religious men who were coming from Palestine into England.

Albert, the Holy Patriarch of Jerusalem, having given a written rule to the Carmelite friars about the year 1205, some brothers of this order were soon after brought over from mount Carmel by John lord Vescy and Richard lord Gray of Codnor, when they returned from the Holy Land.  In 1212 Simon, who had then lived a recluse twenty years imitating the Marcariuses and Arseniuses in the most heroic practices of penance and contemplation, was much affected with the devotion of these servants of God to the blessed Virgin, their edifying deportment, and their eremitical austere institute, and joined their holy company before the end of the year 1212.

After his admission he was sent to Oxford to finish his studies; and having run through his academical course he returned to his convent, where so bright was the example of his piety, that the virtue of the rest seemed to suffer an eclipse by the extraordinary lustre of his sanctity.

St. Simon governed the order with great sanctity and prudence during twenty years, and propagated it exceedingly from England over all Europe being himself famous for his eminent virtue, and a great gift of miracles and prophecy.  He wrote several hymns and decrees for his order, and useful things for its services says Leland.

At length, in the hundredth year of his age, having France, he sailed to Bordeaux, where God put an end to his labors some months after his arrival, in 1264, on the 16th of July.  He was buried in the cathedral of that city, and was honored among the saints soon after his death.  Pope Nicholas III, granted an office to be celebrated in his honor at Bordeaux on the 16th of May, which Paul V. extended to the whole order.