Mary Elizabeth Grey, Countess Grey (née Ponsonby; 4 March 1776 – 26 November 1861) was a British aristocrat and political hostess.

Mary Elizabeth Ponsonby was born on 4 March 1776 in Whitehaven.

She married on 18 November 1794 Charles Grey MP (1764–1845), the future 2nd Earl Grey and Prime Minister of the United Kingdom of Great Britain and Ireland.

They had ten sons and six daughters: Charles Grey, 2nd Earl Grey, was Prime Minister of the United Kingdom of Great Britain and Ireland from 22 November 1830 to 16 July 1834.

She lived until 26 November 1861, when she died aged 85 in Eaton Square, London.