Marie-Madeleine Lachenais, known as Joust (Arcahaie, Haiti 1778 – Kingston, Jamaica 22 July 1843), was a de facto Haitian politician. She was the mistress of president Alexandre Sabès Pétion and president Jean-Pierre Boyer and exerted a significant influence over the affairs of state during their presidencies, for a period 36 years (1807–1843).
Marie-Madeleine Lachenais was the daughter of Marie Thérèse Fabre and the French colonel de Lachenais. She had a relationship with Alexandre Petion, with whom she had two daughters, Celie and Hersilie. In 1807, Alexandre Petion became president, and she acted as his adviser. Petion appointed Jean-Pierre Boyer as his successor with her support. After his installment in 1818, she functioned as mistress and political adviser to Boyer as well and had a daughter, Azema, with him. Her will affected the acts passed in parliament between 1818 and 1840. In 1838, she persuaded Boyer to remain as president when he contemplated to step down. She also revealed and prevented a planned coup, in which Faustin Soulouque was involved. After the deposition of Boyer in 1843, Lachenais and her daughters were escorted to a ship to follow Boyer in his exile to Jamaica.