Polling stations opened at 7 a.m. for voters to elect 460 new MPs and 100 senators for a four-year term.
The ballot was being held at 31,497 polling stations in 41 electoral districts across the country. Some 29 million Poles aged 18 and over were eligible to vote.
The official results of the election were expected to be announced by Tuesday.
More than 600,000 Poles living abroad have registered to vote by absentee ballot, according to the Polish foreign ministry.
Amid a media blackout that began on Friday at midnight, domestic news organisations were prohibited from publishing opinion polls showing the level of support for candidates.
Under Polish law, such a ban lasts until polling stations close. Political campaigning is also forbidden during this period.
Breaking the rules is punishable by a fine of up to PLN 1 million (EUR 220,000, USD 230,000).
(gs)
Source: Polish Radio, IAR, PAP, wybory.gov.pl