Like many other young men of good birth Thomas Dudley became a page, in his case in the household of William, Baron Compton at nearby Castle Ashby. Later he raised a company of men following a call to arms by Queen Elizabeth, and served in the English army led by Sir Arthur Savage fighting with King Henry IV of France during the French Wars of Religion. He fought the Spanish at the Siege of Amiens in 1597 which in September surrendered and was the final action of the war.