Mornay was gradually recognized as Henry's right-hand man, representing him in England from 1577 to 1578 and again in 1580, and in the Low Countries 1581-1582. With the death of the Duke of Alençon-Anjou in 1584, by which Henry was brought within sight of the throne of France, the period of Mornay's greatest political activity began, and after the death of Henry I, Prince of Condé, in 1588, his influence became so great that he was popularly styled the "Huguenot pope". He was present at the siege of Dieppe, fought at Ivry, and was at the siege of Rouen in 1591-92 until he sent on a mission to the court of Queen Elizabeth. Both he and his wife befriended English Protestants like Francis Walsingham, Mary Sidney, and her brother Philip Sydney.