A priest hunter was a person who, acting on behalf of the English and later British government, spied on or captured Catholic priests during Penal Times. Priest hunters were effectively bounty hunters. Some were volunteers, experienced soldiers or former spies.

As the Catholic bishops from the reign of Queen Mary were dead, imprisoned or in exile, and those priests they had ordained were dying out or converting to Protestantism, William Allen conceived the idea for a seminary for English Catholic priests at Douai, where several of the chief posts were held by refugee professors who had fled Oxford University upon the reimposition of Protestantism in England. The English College at Douai was founded as a Catholic seminary in 1569. Similar colleges also came about at Douai for Scottish and Irish Catholic clergy, and also Benedictine, Franciscan and Jesuit houses. Other English seminaries for the training of priests from and for England and Wales included those in Rome (1579), Valladolid (1589), Seville (1592) and Lisbon (1628).

Elizabeth I reinstated the Protestant Bible and English Mass, yet for a number of years, she refrained from persecuting Catholics. After the Rising of the North of 1569 and the papal bull Regnans in Excelsis (1570), plus the threat of invasion by Catholic France or Spain assisted by English Catholics, the Crown was led to adopt ever-increasing repressive measures.

The Bulls, etc., from Rome Act 1571 not only forbade the publishing of any documents from the Pope, but also the importation and distribution of crosses, beads, pictures, and tokens called "Agnus Dei" (a Lamb of God sealed upon a piece of wax from the Paschal candle blessed by the Pope). From the 1570s missionary priests from continental seminaries came to England secretly. In the autumn of 1577, Queen Elizabeth's Principal Secretary, Francis Walsingham canvassed the Anglican bishops for a list of recusants in their dioceses and how much each was worth. Cuthbert Mayne (1544–1577) was the first English Catholic "seminary priest" to be executed under the laws of Elizabeth I.

The Religion Act 1580 fined and imprisoned those who celebrated the Mass or attended a Mass. The Jesuits, etc. Act 1584 commanded all Catholic priests to leave the country in forty days or be punished for high treason unless, within the 40 days, they swore an oath to obey the Queen. Those who harboured them, and all those who knew of their presence and failed to inform the authorities, would be fined and imprisoned for felony. It also provided an incentive to informers by according them one-third of any forfeitures.

This Act was followed by another, the Jesuits, etc. Act 1584, which declared that anyone ordained a priest outside the Queen's dominions who then came into the country was deemed a traitor, and anyone harbouring them, a felon. Nicholas Woodfen (Devereux) and Edward Stransham, who had both studied at the English College, Douai, were executed at Tyburn on 21 January 1586.

One of the most infamous priest hunters of Elizabeth's reign was Sir Richard Topcliffe, who delighted in personally torturing and playing mind games with the priests whom he apprehended. Described by Father John Gerard as "old and hoary and a veteran in evil", Topcliffe ultimately fell from favour with the Queen and was imprisoned very soon after his role in the arrest, trial, and execution of the underground priest and secret poet, Fr. Robert Southwell, S.J.

Walsingham tracked down Catholic priests in England and supposed conspirators by employing informers and intercepting correspondence. Shortly before setting off for England, Edmund Campion learned that a letter detailing their party and mission had been intercepted and that they were expected in England. It was a common practice for a spy to pose as a Catholic and engage a suspect in conversation in the hope of eliciting an incriminating statement. This technique led to the arrest and execution of Richard Simpson in 1588.