Stanisław Małachowski (born Aug. 24, 1736, Końskie, Pol.—died Dec. 29, 1809, Warsaw, Duchy of Warsaw [now in Poland]) was a Polish statesman who presided over Poland’s historic Four Years’ Sejm, a constituent Diet that met in 1788–92.
The son of Jan Małachowski, the royal grand chancellor, Małachowski was named marshal (speaker) of the Sejm (Diet) in 1788. He was the prime force behind a constitution, adopted in 1791, that embodied such modern western European reforms as majority rule in parliament, separation of powers, and enfranchisement of the middle classes; this constitution was abrogated at the Second Partition of Poland in 1792. In 1807–09 Małachowski served as president of the senate (government) of the Duchy of Warsaw, promoted by Napoleon.