Mary Degg was the daughter of Captain William Degg, a British army officer, and Catherine Meighen. Mary’s mother died within months of the birth, and her father then remarried while serving in Ireland. On 1 January 1756, Mary married Lord Robert Manners, and within days of their wedding she and her new husband were presented to the King. Mary was described as a great beauty. An imposing portrait of her in later life was painted by Sir Thomas Lawrence in 1826 and is also in the collection of the National Galleries of Scotland.