Szymon Marcin Kossakowski (Lithuanian: Simonas Martynas Kosakovskis; 1741 in Šilai, Jonava – 1794) was a Polish–Lithuanian nobleman (szlachcic), and one of the leaders of the Targowica Confederation. In 1793, he became the last Great Hetman of Lithuania.
He participated in the Radom Confederation and the Bar Confederation. A supporter of the Russian Empire during the Kościuszko Uprising and earlier, he was deemed a traitor. In the aftermath of the Wilno Uprising he tried to escape by boat, but was captured and hanged in the town hall square of Wilno with the inscription of He who swings will not drown and was buried in the cellars of the church in Jonava.