Sir Thomas was an early convert to Protestantism, which brought him into prominence when Edward VI came to the throne. During the protectorate of Edward Seymour, 1st Duke of Somerset, he entered public life and was made the Secretary of State, and was sent on an important diplomatic mission to Brussels. In 1548 he was knighted. On the accession of Queen Mary I he lost all his offices, but in the reign of her sister, Elizabeth I, he was prominently employed in public affairs.