He was born in Maxfield, a parish of Guestling, near Winchelsea, in Sussex, an historic county of South East England, and entered as one of the original scholars of St John's College, Oxford, in 1557.

Among those who also entered at the beginning was Edmund Campion, the Jesuit martyr; at this period of his life, he conformed to the Established Anglican Church, and was ordained as a deacon.

When he found it necessary to quit the university, he was tutor in the family of the Duke of Norfolk, where he had among his pupils Philip, Earl of Arundel, also subsequently martyred.

In the meantime, Gregory Martin left the house of the Duke of Norfolk, and crossing the seas, presented himself at Dr Allen's College at Douai as a candidate for the priesthood, in 1570.

Campion was now a professed Catholic, and he received minor orders and the subdiaconate, after which he proceeded to Rome and eventually entered the Society of Jesus.

Thomas Worthington, Richard Bristow, William Rainolds, and Allen himself were to assist in revising the text and preparing suitable notes to the passages which were most used by the Protestants.