Poles will vote in a closely contested race that pits pro-EU centrist Warsaw Mayor Rafal Trzaskowski against nationalist contender Karol Nawrocki, who draws inspiration from US President Donald Trump and is backed by the main opposition Law and Justice (PiS) party.
The rivals are neck and neck in opinion polls.
The runoff setting reflects the duopoly of centrists and nationalists that has dominated Polish politics for two decades.
The election is taking place against a backdrop of rising anti-establishment sentiment in Poland, with the far-right achieving their strongest ever showing.
In Poland, the job of president is largely ceremonial, but comes with crucial veto power.
A Trzaskowski victory would give the government a major boost, while a Nawrocki win would reinforce its difficult cohabitation with the president.
(mo/gs)
Click on the audio player above for a report by Michał Owczarek.