The Partition Sejm was a Sejm lasting from 1773 to 1775 in the Polish–Lithuanian Commonwealth, convened by its three neighbours in order to legalize their First Partition of Poland. During its first days in session, that Sejm was the site of Tadeusz Rejtan's famous gesture of protest against Partition. The Sejm also passed other legislation, notably establishing the Permanent Council and the Commission of National Education. Cardinal Laws were confirmed.

The First Partition of Poland took place in 1772 as the first of three partitions that eventually ended the existence of the Polish–Lithuanian Commonwealth by 1795. The growth of power in the Russian Empire threatened the Kingdom of Prussia and the Habsburg monarchy and was the primary motive behind the First Partition.