Her father, Charles I, wished the Princess Royal to marry a son of Philip IV, king of Spain, while her first cousin, Karl Ludwig, the Elector Palatine, was also a suitor for her hand. Both proposals fell through and she was betrothed to Willem, the son and heir of Frederick Henry, Prince of Orange and Stadtholder of the United Provinces, and of Amalia of Solms-Braunfels. The marriage took place on 2 May 1641 at the Chapel Royal, Whitehall Palace, London. The marriage was not consummated for several years due to the bride's age when married: nine. In 1642, Mary moved to the Dutch Republic with her mother, Queen Henrietta Maria, and in 1644, as the daughter-in-law of the stadtholder, Frederick Henry, she became visible in courtly and public events.