Cuthbert Mayne was born in north Devon, raised in the Elizabethan religious settlement, ordained in the Anglican Church, and was chaplain of St. John's College, Oxford. There, under the influence of his fellow Oxford clergymen including Edmund Campion (then still a deacon of the established church) and Gregory Martin, he began his journey into the Catholic Church. In 1573, like Campion, he left Oxford for the English seminary at Douai in the Spanish Low Countries.
He was ordained a Catholic priest in 1575 — one of the first generation of seminary priests trained at Douai by Cardinal Allen specifically for clandestine return to the Elizabethan English mission. He returned to England in April 1576 with the alias 'Mr. Bourne' and served as chaplain to the recusant Tregian family at Golden Manor in Cornwall.
He was arrested on June 8, 1577 — the first seminary priest captured in England — tried at Launceston Castle for the relatively novel charge of importing 'agnus dei' devotional articles from the Continent and saying Mass (then under the 1571 Act treason), and convicted on perjured evidence. He was hanged, drawn, and quartered at Launceston market square on November 30, 1577. He was the first of about 130 English seminary priests martyred in the Elizabethan and Jacobean persecutions — the inaugural witness of the Douai English mission. His skull was preserved at the Tregian-affiliated Lanherne convent in Cornwall and remains in Catholic possession to this day.