During the Italian War of 1551–1559, Herbert commanded the English army sent to France in support of Spain. His troops did not arrive in time for the Battle of St. Quentin (1557), but played a significant role in the capture of the city afterwards. Pembroke was Mary's most effective commander in the war with France. Mary sometimes suspected Pembroke's loyalty, but he was employed as governor of Calais, as president of Wales and in other ways. He was also to some extent in the confidence of Philip II of Spain. The earl retained his place at court under Elizabeth I until 1569, when he was suspected of favouring the projected marriage between Mary, Queen of Scots, and the Duke of Norfolk.