When Margaret's father succeeded as 30th Earl of Mar in 1965 she became Lady Margaret of Mar, and her brother became The Master of Mar, Lord Garioch. When Lord Garioch died in 1967, Margaret became The Mistress of Mar as the elder heir-portioner presumptive in general of her father.
Countess of Mar
When in 1975 her father the 30th Earl died, Lady Margaret became the 31st holder of the Mar earldom, the premier earldom of Scotland, and entered the House of Lords, making her maiden speech in April 1976. After the passing of House of Lords Act 1999, Lady Mar was elected to serve as one of the ninety-two hereditary peers retained in the House, where she sat as a crossbencher, meaning she is not aligned with any particular political party. She retired from the House on 1 May 2020. Lady Mar held a number of positions within the House of Lords:
Deputy Chair of Committees 1997–2007
Select Committee on European Communities Sub-Committee C 1997–1999
Deputy Speaker 1999–2007, 2009–2012 and 2014–2020
Select Committee on European Union Sub-Committee D 2001–2005
Lady Mar was also a member of the Joint Committee on Statutory Instruments, a member of the Lords Refreshment Committee, and a member of the panel of Deputy Chairmen of Committees. Lady Mar was also secretary of the All Party Parliamentary Group on Pesticides and Organophosphates. Lady Mar has also held a variety of non-political offices:
In the summer of 1989, while dipping her sheep through a tank of organophosphorous chemicals, Lady Mar was subjected to a splash of chemicals on her foot, and three weeks later developed headaches and muscular pains. She was eventually diagnosed with chronic fatigue syndrome. Since then Lady Mar has used her seat in the House of Lords almost exclusively to press the government to provide suitable care and support for patients with similar long-term and poorly understood medical conditions, and to better regulate the use of organophosphates. This also led to her membership on the EU sub-committees listed above. As a consequence of her illness, Lady Mar founded the organisation to co-ordinate the activities of a fairly broad spectrum of charities and voluntary organisations working with patients with chronic fatigue syndrome, which is also known as myalgic encephalomyelitis.
Family
Lady Mar has married three times: first to Edwin Noel Artiss, then to John Salton, and finally to John Jenkin. From the first marriage she had a daughter: Susan Helen of Mar, Mistress of Mar, the heir presumptive to her mother's peerage. Lady Susan is married to Bruce Alexander Wyllie, and has two daughters, Isabel and Frances.