The institution of interrex existed in the Polish-Lithuanian Commonwealth, whose ruling classes liked to view their Republic (Rzeczpospolita) or Commonwealth as an heir to Roman republican traditions. The Commonwealth's monarch holding a double title of the Two Nations King of Poland and Grand Duke of Lithuania entered upon their office by free election (wolna elekcja), which often led to a relatively long interregnum. Since 1572, the role of interrex traditionally fell to the Archbishop of Gniezno and Primate of Poland of the Roman Catholic Church. The Archbishop could nominate a replacement (traditionally he would choose the bishop of Kujawy).
The interrex would represent the country on the international scene and oversee the internal administration until a new king was elected. In special circumstances he could declare war and negotiate peace. He summoned and presided over the convocation sejm and the election sejm, the gathering of nobility that elected the king. He also announced the election of the king.
|Interreges of the Commonwealth|
|Took the office of interrex in
||Gave up the office of interrex in
|1574||1575||Jakub Uchański (again)|
|1673||1674||Kazimierz Florian Czartoryski|
|1674||1674||illness and death of Kazimierz Florian Czartoryski led to him being replaced by the bishop of Kraków, Andrzej Trzebicki and bishop of Poznań, Stefan Wierzbowski|
|1696||1697||Michał Stefan Radziejowski|
|1704||1705||Michał Stefan Radziejowski (again)|
|1704||1705||Michał Stefan Radziejowski was stripped of his authority by the Pope and went into hiding. He was replaced by bishop of Poznań, Mikołaj Święcicki|
|1733||1734||Teodor Andrzej Potocki|
|1763||1764||Władysław Aleksander Łubieński|