Polling stations opened at 7am and close at 9pm.
The ballot is being held at 27,415 polling stations in 41 electoral districts across Poland.
Some 30.7 million Poles are eligible to vote.
There are 5,114 candidates vying for a seat in the lower house of parliament, or 11 candidates per seat.
Two hundred and seventy-eight senator hopefuls are running for a seat in the upper house, or three candidates per mandate on average.
Members of the Polish community based in the United States voted on Saturday. Some 31,928 voters registered there.
A ban on political campaigning and restrictions on what the media can report are in force until the last polling station closes.
Canvassing is forbidden at this time. In practice, this means that public gatherings, encouraging voters to vote in a certain way, distributing election materials or publishing poll results are banned.
Breaking the rules is punishable by a fine of up to PLN 5,000 (EUR 1,160, USD 1,277). Publication of election polls is liable to a fine ranging from PLN 500,000 to one million.
Source: IAR, PAP