Margaret was the daughter of David Wemyss, 2nd Earl of Wemyss and Margaret Leslie, daughter of John Leslie, 6th Earl of Rothes. She was the youngest of sixteen children; she and her older sister, Lady Jean Wemyss (a half-sister by her father's first wife), were the only ones who did not die young and childless.
Margaret was a daughter of David Wemyss, 2nd Earl of Wemyss, and Margaret Leslie, daughter of John Leslie, 6th Earl of Rothes. She was one of sixteen siblings; she and her older sister, Lady Jean Wemyss (a half-sister by her father's first marriage), were the only ones who did not die young or become childless.