Margaret of Norfolk or Margaret of Brotherton, Duchess of Norfolk in her own right, was the daughter and eventual sole heir of Thomas of Brotherton, eldest son of King Edward I of England by his second marriage. In 1338, she succeeded to the earldom of Norfolk and the office of Earl Marshal. In 1397, she was created Duchess of Norfolk for life.

Thomas of Brotherton, 1st Earl of Norfolk, was the fifth son of King Edward I of England (1239–1307), and the eldest child by his second wife, Margaret of France, the daughter of King Philip III of France. He was, therefore, a younger half-brother of King Edward II and a full brother of Edmund of Woodstock, 1st Earl of Kent. He occupied the office of Earl Marshal of England.