Poland's governing Law and Justice party (PiS) has won Sunday's parliamentary election, with most of the results now counted.
The conservative nationalist party has nearly 44% of the vote, enough to boost its majority in the lower house.
Main rival the centrist Civic Coalition (KO) had about a quarter of the vote.
PiS has been at loggerheads with the EU over reforms to Poland's judiciary and has also been criticised over its position on gay rights.
"We have victory," jubilant PiS leader Jaroslaw Kaczynski told supporters at party headquarters in Warsaw late on Sunday.
"We have four years of hard work ahead. Poland must change more and it must change for the better."
During its first term in office, the party put in place generous welfare programmes, boosting its support among poorer voters.
Measures included a popular child allowance, tax breaks for low-income earners and increases to pensions and the minimum wage.
"The PiS is finally taking care of the weakest, most vulnerable members of society," Kasia, a 40-year-old psychologist working at a women's shelter, told AFP news agency after voting in Warsaw on Sunday. "I've seen it first hand at work."
A party that delivers
By Adam Easton, BBC News, Warsaw
Law and Justice seems to have won the highest percentage of votes since democracy was restored here in 1989.
The party will have a slightly increased majority and a strong mandate to continue its socially conservative programme.
Law and Justice has pledged to continue its controversial reform of the judiciary despite opposition from the European Commission, which says the independence of Poland's judges is being eroded. That issue has not dented Law and Justice's popularity.
Instead the party has reaped the rewards of its generous welfare scheme, which has benefitted millions of families. For the first time in years, it has proposed a balanced budget for next year despite economists' warnings that the scheme would ruin public finances.
Law and Justice now has a reputation of a party that delivers on its promises.
Results from 99% of constituencies published on Monday suggest an increase for PiS on the 231 MPs they currently hold in the 460-seat lower house to 239.
The state electoral commission will announce the breakdown of parliamentary seats with the final official result, which is expected later on Monday.
It is not yet clear whether PiS will retain its majority in the upper house, the Senate.
Exit polls suggested turnout was more than 60%.
The left-wing coalition Lewica is expected to come third. Lewica was also celebrating its predicted result after left-wing parties lost their seats four years ago due to fragmentation.
Robert Biedroń, one of the bloc's three co-leaders and Poland's first openly gay lawmaker, told a rally: "We are returning to parliament. We are going back to where the Polish left has always belonged."
LGBT rights became the single biggest cultural issue ahead of the election. PiS - and the Roman Catholic Church - maintain that gay rights are a threat to traditional Polish families and values.
A year ago, the EU ordered Poland halt the application of a new law which critics said would have given PiS political control of the Supreme Court.
The governing party had argued that reforms were needed to remove judges appointed during the communist era and to make the court more efficient.
But the European Commission - the EU's executive arm - argued the reforms undermined the rule of law by giving the governing party control of the judiciary.