Louisa Petty, Marchioness of Lansdowne (née Lady Louisa FitzPatrick; later Petty Fitzmaurice; 1755 – 7 August 1789), known as the Countess of Shelburne from 1779–84, was an Anglo-Irish aristocrat from the Mac Giolla Phádraig dynasty.

[1] The Marchioness was the youngest daughter of John FitzPatrick, 1st Earl of Upper Ossory, and his wife, Lady Evelyn (née Leveson-Gower; daughter of John Leveson-Gower, 1st Earl Gower).

She had a younger brother Richard, who also became a noted statesman and soldier, and an elder sister, Lady Mary Fox (Baroness Holland), the subject of paintings by Thomas Gainsborough, Sir Joshua Reynolds, and Pompeo Batoni.

[2][3] She married, as his second wife, William Petty, 2nd Earl of Shelburne, who served as Prime Minister for 10 months in 1782–83, and was afterwards created Marquess of Lansdowne.

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