His life, according to the Golden Legend of James of Voragine, as Englished by William Caxton:
In the year of our Lord five hundred and thirty-seven, there was a man named Theophilus which was vicar of a bishop, as Fulbert saith, that was bishop of Chartres. And this Theophilus dispended all wisely the goods of the church under the bishop; and when the bishop was dead, all the people said that this vicar should be bishop. But he said the office of vicar sufficed him, and had liefer that than to be made bishop, so there was there another bishop made, and Theophilus was against his will put out of his office. Then he fell in despair, in such wise that he counselled with a Jew how he should have his oflice again, which Jew was a magician, and called the devil, and he came anon. Then Theophilus, by commandment of the devil, denied God and his Mother, and renounced his Christian profession, and wrote an obligation with his blood and sealed it with his ring, and delivered it to the devil, and thus he was brought into his office again. And on the morn Theophilus was received into the grace of the bishop by the procuration of the devil, and was re-established in the dignity of his office. And afterwards, when he advised himself, he repented and sorrowed sore of this that he had done, and ran with great devotion unto the Virgin Mary, with all devotion of his thought, praying her to be his aid and help. And then on a time our blessed Lady appeared to him in vision, and rebuked him of his felony, and commanded him to forsake the devil, and made him to confess Jesu Christ to be son of God, and to knowledge himself to be in purpose to be a christian man, and thus he recovered the grace of her and of her son. And in sign of pardon that she had gotten him, she delivered to him again his obligation that he had given to the devil, and laid it upon his breast so that he should never doubt to be servant of the devil, but he enjoyed that he was so delivered by our blessed Lady. And when Theophilus had heard all this he was much joyful, and told it to the bishop and tofore all the people that was befallen him, and all marvelled greatly, and gave laud and praising unto the glorious Virgin, our Lady, Saint Mary. And three days after he rested in peace.