Born Mary Monckton, probably at Serlby Hall, Nottinghamshire, the family seat, she was a daughter of John Monckton, 1st Viscount Galway by his second wife, Jane Westenra of Rathleagh, Queen's County, Ireland.

[1] Boswell places Mary Monckton among the bluestocking clubs,[2] and writes:Johnson was prevailed with to come sometimes into these circles, and did not think himself too grave even for the lively Miss Monckton (now Countess of Corke), who used to have the finest bit of blue at the house of her mother, Lady Galway.

Politically, there was never any doubt of her sympathies: although brother Edward wavered, Mary still signed herself "a True Whig" into old age.

[4] Several of the historical novels of Georgette Heyer refer to the fame of her literary parties, and the crucial role which wit and good conversation played there: a character remarks that the highest praise a hostess can dream of is to be called "a second Lady Cork".

She was buried in Brewood parish church, Staffordshire, close to the estates of her brother, Edward Monckton.