The Duchess was the second daughter of John Gunning and the Hon. Bridget Bourke, of Castle Coote, county Roscommon, Ireland, and was by repute one of the greatest beauties of the Court of George III. She was the widow of James [d. 1758], 6th Duke of Hamilton, whom she married on 14 February 1752. They had three children: James George (7th Duke), Douglas (8th Duke), and Elizabeth. On 3 March 1759 she married secondly, to the 5th Duke of Argyll, by whom she had five children: George John (Earl of Campbell), George William (6th Duke of Argyll), John Douglas Edward Henry (7th Duke of Argyll), Augusta, and Charlotte Susan Maria. She was created Baroness Hamilton in her own right on 20 May 1776. The Duchess commissioned Joshua Reynolds to paint a portrait (now in the NGA) of her daughter, Lady Elizabeth, who was five years old when she sat to the artist in February 1758. Her father the Duke had died only a month before. Her residence at Hambleton may have dated only from after her second marriage, or after she was created Baroness.