Marie Louise Mignot (1712–1790), commonly known as Madame Denis, was the niece and long-time companion of the French Enlightenment writer and philosopher Voltaire.
Born in Paris, she was the daughter of Voltaire’s elder sister, Catherine Arouet, and Nicolas-Charles Mignot. In 1735, she married Nicolas-Charles-Joachim Denis, a commissary in the French war office. After the death of her husband in 1744, she established a close relationship with Voltaire. Following the death of Voltaire's mistress and intellectual partner, Émilie du Châtelet, in 1749, Mignot became his primary domestic companion and housekeeper.
Mignot lived with Voltaire during his residences at Les Délices in Geneva and later at his estate in Ferney. Their relationship was a subject of historical scrutiny; surviving correspondence confirmed that their bond was romantic and sexual in nature, despite the familial connection. In addition to managing Voltaire's household and hosting the many visitors who traveled to see him, Mignot maintained her own literary interests, writing several plays, such as La Coquette punie (1752).
Upon Voltaire's death in 1778, Mignot was the principal heir to his significant estate. She was responsible for the negotiation and sale of Voltaire’s personal library to Catherine the Great of Russia, which is now preserved in the National Library of Russia in Saint Petersburg. In 1780, at the age of 68, she married François Duvivier, a captain in the cavalry. She died in Paris in 1790.