The Constitution of 3 May 1791 (Polish: Ustawa Rządowa, "Governance Act"), was a constitution adopted by the Great Sejm ("Four-Year Sejm", meeting in 1788–92) for the Polish–Lithuanian Commonwealth, a dual monarchy comprising the Crown of the Kingdom of Poland and the Grand Duchy of Lithuania. The Constitution was designed to correct the Commonwealth's political flaws and had been preceded by a period of agitation for—and gradual introduction of—reforms, beginning with the Convocation Sejm of 1764 and the consequent election that year of Stanisław August Poniatowski as the Commonwealth's last king.
The Constitution sought to implement a more effective constitutional monarchy, introduced political equality between townspeople and nobility, and placed the peasants under the protection of the government, mitigating the worst abuses of serfdom. It banned pernicious parliamentary institutions such as the liberum veto, which had put the Sejm at the mercy of any single deputy, who could veto and thus undo all the legislation that had been adopted by that Sejm. The Commonwealth's neighbours reacted with hostility to the adoption of the Constitution. King Frederick William II broke Prussia's alliance with the Polish-Lithuanian Commonwealth and joined with Catherine the Great's Imperial Russia and the Targowica Confederation of anti-reform Polish magnates to defeat the Commonwealth in the Polish–Russian War of 1792.
The 1791 Constitution was in force for less than 19 months. It was declared null and void by the Grodno Sejm that met in 1793, though the Sejm's legal power to do so was questionable. The Second and Third Partitions of Poland (1793, 1795) ultimately ended Poland's sovereign existence until the close of World War I in 1918. Over that 123-year period, the 1791 Constitution helped keep alive Polish aspirations for the eventual restoration of the country's sovereignty.
