Born Margaret Lucas to Sir Thomas Lucas (1573–1625) and Elizabeth Leighton (died 1647), she was the youngest child of the family. She had four sisters and three brothers, the royalists Sir John Lucas, Sir Thomas Lucas and Sir Charles Lucas, who owned the manor of St John's Abbey, Colchester.[2] As a teenager, she became an attendant on Queen Henrietta Maria and travelled with her into exile in France, living for a time at the court of the young King Louis XIV. She became the second wife of William Cavendish, 1st Duke of Newcastle-upon-Tyne in 1645.
Her husband, then-marquess William Cavendish, 1st Duke of Newcastle, was a Royalist commander in Northern England during the First English Civil War and in 1644 went into self-imposed exile in France. Margaret accompanied him and remained abroad until the Stuart Restoration in 1660.[3]
