He studied at Reims and was ordained priest at Soissons, 21 December, 1581, together with the martyrs George Haydock and Robert Nutter. Their ordination coincided with the time that the news of Edmund Campion's death reached the college.
Dean said his first Mass 9 January and left for England 25 January, 1581. He was banished with a number of other priests in 1585, put ashore on the coast of Normandy, and threatened with death if he dared to go back to England. Nevertheless he quickly returned to his mission work there and was again arrested, tried, and condemned for his priesthood, 22 August, 1588.
The failure of the Spanish Armada brought about a fierce anti-Catholic persecution and some twenty-seven Catholics were executed that year. Six new gibbets were erected in London, it is said at the Earl of Leicester's instigation, and Dean, who had been condemned with five other priests and four laymen, was the first to suffer on the gallows erected at Mile End. With him died a layman, Henry Webley, for relieving and assisting him.
At the execution Dean tried to speak to the people, "but his mouth was stopped by some that were in the cart, in such a violent manner that they were like to have prevented the hangman of his wages". Seven Catholics died on the same day. Leicester died on 5 September, within a week of their execution.
- Richard Challoner, Missionary Priests (1741), I, 209;
- Stow, Annales (1615), 749;
- 'Douay Diaries (1878);
- John Morris, Troubles of Our Catholic Forefathers##, II, 72, 156, 157.