Margery Byset (Bisset, Bissett; also Marjery, Margaret, Marie) was an Irish noblewoman belonging to the Bissett family whose marriage to John Mór Tanister MacDonnell in 1399 laid the basis for the Clan Donald claim to the Glens of Antrim, the lordship of which her family had established in the 13th century. She is the ancestress of the Clan MacDonald of Dunnyveg and their powerful descendant sept the MacDonnells of Antrim, through whom she is an ancestor of many of the Irish and British nobility and royalty living today.