Marie Anne de Vichy-Chamrond, marquise du Deffand (1697 – 23 September 1780) was a French hostess and patron of the arts.
She was born at the Château de Chamrond, in Ligny-en-Brionnais, a village near Charolles (département of Saône-et-Loire) of a noble family. Educated at a convent in Paris, she showed great intelligence and a sceptical, cynical turn of mind. The abbess, alarmed at the freedom of her views, arranged for Jean Baptiste Massillon to visit and reason with her, but he accomplished nothing. Her parents married her at twenty-one years of age to her kinsman, Jean Baptiste de la Lande, marquis du Deffand, without consulting her inclination. The marriage was an unhappy one, and the couple separated in 1722.
Madame du Deffand is said by Horace Walpole (in a letter to Thomas Gray) to have been for a short time the mistress of the regent, the duke of Orléans. She appeared in her earlier days to be incapable of any strong attachment, but her intelligence, her cynicism and her esprit made her the centre of attraction of a brilliant circle. In 1721 began a friendship with Voltaire, but their regular correspondence dates only from 1736. She spent much time at Sceaux, at the court of the duchesse du Maine, where she contracted a close friendship with the president Hénault. In Paris she joined the Club de l'Entresol and was the rival of Mme Geoffrin, but the members of her salon were drawn from aristocratic society more than from literary circles. There were exceptions: Voltaire, Montesquieu, Fontenelle and Madame de Staal-Delaunay were among the habitués. When Hénault introduced D'Alembert, Madame du Deffand was captivated by him. She tolerated the encyclopaedists only for his sake.