She is the holder of the original earldom of Mar, the oldest peerage title in the United Kingdom.

[citation needed] From 1959 to 1962, she was a civil servant with the Ministry of Pensions and National Insurance, before taking a position as a nursing auxiliary at the Bromsgrove Cottage Hospital from 1964 to 1969.

When Lord Garioch died in 1967, Margaret became The Mistress of Mar as the elder heir-portioner presumptive in general of her father.

[12] 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.

[16][17][18] Since then Lady Mar 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.