Margaret Mercer Elphinstone

Margaret Mercer Elphinstone, Countess of Flahault, Baroness Keith and Nairne (1788–1867), was a Scottish society hostess.

Margaret, was born in Mayfair on 12 June 1788, the only child of George Elphinstone, 1st Viscount Keith, admiral, and his first wife, Jane, only child and heiress of William Mercer of Aldie, Perth. Upon her mother's death in 1789 she became heiress to the barony of Nairne (then in attainder) and later succeeded to the title.

Margaret was introduced at a young age to the circle of the Princess Charlotte of Wales, to whom she became attached and a close confidante; and this position raised a rumour against her (which, however, she was able entirely to refute) that she betrayed the princess's secrets to the Prince Regent.

On 20 June 1817, at Edinburgh, Margaret married Charles Joseph, comte de Flahaut, Aid-de-Camp to Napoleon Bonaparte, who had been educated in Britain, where he took refuge during the Bourbon Restoration. The Countess held a prominent place in society since her husband held office under the Bonapartes and was Ambassador successively at Rome, at Vienna, and (1860) to the Court of St. James (London), and finally resided at Paris as Chancellor of the Légion d'honneur. The Countess, who was one of the lady patronesses of Almack's and who was a prominent member of polite society, took part in all his social and political work.

The Comtesse died at Palais de la Légion d'honneur in Paris, on 11 November 1867, aged 78. She had five daughters, the eldest of whom (who succeeded to her English, Scots, and Irish titles) was Emily, Dowager Marchioness of Lansdowne at the time of her death succeeded as Lady Nairne.