PiS scored 37.58 percent of the vote, the state electoral commission said.
The panel did not confirm the absolute parliamentary majority projected by exit polls, saying it would publish the distribution of seats on Tuesday.
An exit poll published early Monday gave the PiS 37.7 percent of the vote, translating into a 232-seat majority in the 460-seat lower house of parliament.
The governing Civic Platform (PO) liberals came second with 24.09 percent.
Three other parties also entered parliament, but the left was ousted from the lower house for the first time since the advent of democracy 25 years ago.
An anti-establishment party, Kukiz’15, led by punk rocker Pawel Kukiz made a strong parliamentary debut, capturing 8.81 percent of the vote, in what analysts said was a successful pitch to younger, disillusioned voters.
Another newcomer, the Nowoczesna (Modern) liberal party led by economist Ryszard Petru, scored 7.6 percent of the vote on promises of introducing a 16-percent flat tax.
The PSL farmers’ party, the PO’s junior coalition parter in the outgoing government, scraped past the five percent threshold to enter parliament with 5.13 percent of the vote.
But the United Left, grouping both the ex-communist SLD party and a collection of other left and green parties took 7.55 percent of the vote, less than the eight percent it needed as coalition to enter parliament.
Under the constitution, President Andrzej Duda, elected in May with strong PiS backing, will set the first sitting of parliament after the state election commission confirms seat distribution on Tuesday.
Parliament must meet for the first time before November 24, or within 30 days of the election.
Outgoing Prime Minister Ewa Kopacz must then present her resignation. President Duda will then tap a prime minister-designate to form a government.
Kaczynski’s protege Beata Szydlo is expected to lead the new government.