Gage was born into a long-established recusant family in Surrey: both his parents had been condemned to death and then reprieved for harbouring Catholic priests, while an uncle had been executed for his role in the Babington Plot to assassinate Elizabeth I in 1586.
The eldest was the Royalist soldier Colonel Sir Henry Gage (1597–1645), who fought on the Continent for Catholic Spain and eventually in England for Charles I.
Valladolid was the scene of a good deal of rivalry and bad feelings between the different religious orders, a situation worsened by the temperamental and political tensions between the Spanish and the English.
He joined the Dominicans in Jerez, Spain, taking the religious name Tomás de Santa María, and his pro-Jesuit father disinherited him.
He spent two or three years in the priory in Santiago de los Caballeros, where he seems to have liked the opportunity to study but began to have religious doubts and was led to ask to return to England.
By 1635, with this sum accumulated, Gage, now increasingly disenchanted with Spanish America, was ready to return to Europe, requested permission from the Dominican Provincial, was refused and was posted instead to Petapa.
This journey, lengthened by ill health and wartime conditions, brought him a number of adventures, but also the opportunity to visit Protestant communities in both Germany and France.
Another story recounted with disdain by a Gage who against his vows amassed a fortune, is of the Spanish friar noted for his learning who was excommunicated when money was found in his quarters.
Though for this he was rewarded with the rectorship of Acrise in Kent, he had won for himself general ridicule by a sermon he preached that summer in St Paul's, London, and published in October under the title "The Tyranny of Satan, discovered by the teares of a converted sinner [...] by Thomas Gage, formerly a Romish Priest, for the space of 38 yeares, and now truly reconciled to the Church of England".
In December 1642 he testified against the priest Thomas Holland, whom he had known at St. Omer and Valladolid, and obtained a sentence of hanging, drawing and quartering which was effectively carried out.
Gage then set about publicizing his life's experience, and published his now-famous book, The English-American his Travails by Sea and Land in 1648, which was as much a political pamphlet and an adventurer's prospectus as a traveller's tale.
The execution of Wright was not popular and Gage's treachery, compounded by his attack on his late brother Henry's good name, earned even the rebuke of the court.
In 1651 came an attempt to win back some public regard with his A duell betvveen a Iesuite and a Dominican : begun at Paris, gallantly fought at Madrid, and victoriously ended at London, upon fryday the 16-day of May, Anno Dom.
In 1648 he published The English-American, or a New Survey of the West Indies, a mixture of some original with plagiarized material, taken in later editions especially from the compilation by the parson Samuel Purchas and from the Hispania Victrix (1552) by Francisco Lopez de Gómara (1511-1562).
If God raised the Puritans to purify England, how much more needing remedy were the Catholic-dominated regions of the Americas, subjugated by what Gage considers their notoriously corrupt clergy?
On the strength of Gage's undoubted experience in the Caribbean and Central America, this appeal was heeded, especially with the ending of the Anglo-Dutch war in 1654 led Cromwell to be attentive to new foreign policy openings.
In a secretly planned operation, a force of 18 warships, 20 transport vessels and 3,000 men set sail from Portsmouth on Christmas Day 1654 with Gage on board as chaplain and guide and arrived at Barbados a month later.
An additional 6,000 troops, untrained and badly disciplined, were raised from servants and freemen in the colonies of Barbados, Montserrat, Nevis and St Kitts.
Though Spain formally ceded Jamaica to England in 1670, the maroons (enslaved Africans freed by their Spanish masters) harassed the English efficiently into the 18th century.