In 1553, when Catholic Queen Mary I took the throne upon her younger brother's death, Francis found himself fleeing England along with hundreds of other zealous Protestants who feared the Roman Church's influence in the country. He lived in Italy for five years, continuing to study law and a number of languages - including Italian and French - skills that would prove useful for his later career as a statesman and diplomat at court. As was a common theme with Englishmen of the reformed faith, he returned to England when Elizabeth I succeeded her sister in 1558, and found himself elected to her parliament in January 1559. His court career had begun.
It's unclear just how purposeful Francis's involvement in intelligence began, but towards the end of the 1560s, he had begun working for Sir William Cecil, the queen's secretary. Through this work, he began to uncover hints at a Catholic plot to overthrow the Protestant Elizabeth in favor of her cousin, Mary, Queen of Scots. He dove into uncovering the details of this plot, and his inexperience at spy work proved obvious when he falsely believed the innocence of a London banker, Roberto Ridolfi, whom he had been interrogating for his involvement in the plot. This naivety led to missing a crucial opportunity to uncover the Duke of Norfolk's treason, and Ridolfi's significant hand in passing dangerous and threatening letters on the Scottish queen's behalf. Norfolk would later be executed, but this delay in uncovering the depth of the nobleman's treason was a personal failure for Walsingham. Around this time, he coined a phrase that would define his career: "there is lesse daynger in fearinge to much than too lyttle."
At this point, Walsingham's spy network and intelligence work took off. Not content to sit back while plots to murder Elizabeth and place Catholic Mary on the throne, he created a vast network of undercover spies, and sent them across the continent - even into northern Africa. Through a wide variety of intelligence-gathering tactics, such as bribery, interrogation, torture, threats (such as occasional use of the rack), and psychological games, Walsingham managed to successfully uncover two major Elizabethan plots - first the Throckmorton Plot in 1583, and then the Babington Plot of 1586, which directly led to the execution of Mary, Queen of Scots. His final intelligence maneuvers would prove extremely useful in the coming war against Spain, as several of his spies would provide detailed reports of the Spanish plans for the Armada invasion of 1588.
By this time, Walsingham was elderly by Elizabethan standards, and apparently in considerable debt at the time of his death on 6 April 1590. His legacy as one of history's great men of British intelligence, is clouded by secrecy (as the nature of the job requires) and thus few of his methods are known to this day. But it is clear that he played a vital role in defending Elizabeth I's throne, forging the later unification of England and Scotland, and helping to neutralize foreign threats during Elizabeth's reign. He was well-respected for his role as spymaster, earning this description from English chronicler, William Camden: "[He was] a most subtle searcher of hidden secrets, who knew excellently well how to win men's minds unto him... He saw every man, and none saw him."