Polls open at 7 a.m. (5:00 GMT) and close at 9 p.m. All seats in the upper-house Senate and the lower-house Sejm are up for grabs.
The ruling conservative Law and Justice party will be seeking a third term, aided by smaller allies, who together form a coalition called United Right. They will be challenged by the Civic Coalition, a center-right opposition alliance led by former EU boss Donald Tusk.
Also running are the social conservative Third Way, made up of the centrist Poland 2050 and the agrarian Polish People's Party, as well as the center-left Newly Left and the far-right Confederation, which has been calling for an end to unconditional support for Ukraine.
The ruling Law and Justice is in the lead in all major opinion polls, but is projected to fall short of an overall majority. The second-placed Civic Coalition, which is seeking to mend Poland’s strained ties with the EU, may have a shot at forming a coalition government with Third Way and New Left, while the Confederation may become a kingmaker if it sides with Law and Justice.
Poles will also be invited to vote in a referendum called by Law and Justice to ask for public opinion on a range of issues, from raising the retirement age to the admission of African immigrants and the potential sale of state assets to foreign entities.