Son of a loyal courtier, Sir John Seymour (d.1536). Fought in France in 1523 and subsequently knighted. Made an Esquire of the Body in 1531 and a Gentleman of the Privy Chamber in 1536, a few months before his sister Jane's marriage to the King. Appointed Lord High Admiral in 1542 and Lord Great Chamberlain in 1543. Present at the siege of Boulogne in 1544, where his role is said to have been decisive in the city's capture. As Lord Protector, played a key role in the early government of his nephew, Edward VI. Becoming increasingly unpopular with other members of the governing council, he was deposed in 1550, charged with high treason in 1551 and executed in January 1552.