By 1626, when this portrait was commissioned, Lady Mary Erskine was twenty nine years old, and had already been married an incredible seventeen years. She was the daughter of the 2nd Earl of Mar, who was High Treasurer of Scotland and a friend of King James VI and I. In 1609, aged only twelve, she married William Keith, 5th Earl Marischal, and went on to have four children. Jamesone’s clientele encompassed the leading nobility of Scotland, and he was on unusually intimate terms with the Erskine family. As well as painting Lady Mary, he painted her first son William Keith, 5th Earl Marischal, and her third son George Keith became godfather to Jamesone’s son. The richness and refinement of surface detail in this portrait, is exceptional in Jamesone's surviving work.