On 2 January 1554 he was appointed to meet the Spanish ambassadors who had come to London to negotiate a marriage between Queen Mary I and King Philip II of Spain. Wyatt's rebellion broke out on 25 January, and Howard was among those who raised the militia to defend London. On 7 February 1554 he held Ludgate, preventing the rebels from entering the city and leading to their surrender a few hours later. He was appointed to Queen Mary's Privy Council on 3 January 1554, and on 11 March was created Baron Howard of Effingham. On 20 March 1554 he was granted a patent as Lord Admiral, replacing Lord Clinton. On 9 October of that year he was made a Knight of the Garter.