Polish opposition parties are tipped to win a parliamentary majority in Sunday's election that would end eight years of rule by the populist Law and Justice (PiS) party, according to exit polls.
Former EU chief Donald Tusk's Civic Coalition could win 163 seats in the 460-seat parliament and two smaller parties, Third Way and Left, were set for 55 and 30 seats respectively, according to the exit poll.
That would give the three a majority of 248, while PiS is predicted to win 200 seats and the far-right Confederation, its possible coalition partner, was given only 12 seats by the Ipsos exit poll.
"Poland has won, democracy has won," a jubilant Mr Tusk said after the exit poll was released.
"It is the end of this grim period. PiS's reign is over."
The vote will be crucial in determining the future of democracy in the Eastern European country, with PiS introducing a host of measures to muzzle democracy.
PiS has also been an important ally of Ukraine, supplying arms and equipment, and is strongly opposed to Russian expansion.
It has also expanded the Polish army into one of the strongest military forces in Europe, making it a key ally to America and a leading Nato member.
The party has been tough on abortion, migrants and refugees, although it has taken in 1.6 million Ukrainian refugees after the Russian invasion last year.
But it has also said it is the only party that can prevent the “invasion” of refugees.
PiS has come into conflict with the EU on a number of constitutional issues. As a result, Brussels has frozen billions of euros in funding for various projects.
Michal Baranowski, an analyst from the German Marshall Fund, said Poland could now "return to the decision-making centre of the European Union".
Mr Baranowski said the exit poll pointed to a possible "stable opposition government".
Analysts also warned, however, that any governing coalition formed by the opposition could face frequent run-ins with President Andrzej Duda, a PiS ally.
The numbers in the exit poll do not give the potential opposition allies the required three-fifths majority to be able to overturn presidential vetoes.
Turnout was high, with the exit poll estimating the national level at 72.9 per cent, a record for Poland's post-communist history.
"The turnout is probably, and by a lot, the highest" since elections in 1989 when communism ended, said Sylwester Marciniak, head of the National Electoral Office.
Mr Marciniak said some polling stations ran out of ballot papers because of the large crowds and voting had to be extended.
"It's time for a change," said Ewa Bankowska, 43, a finance worker, told AFP as she voted in Halinow, a town just outside the capital Warsaw.
"I'm concerned about the economy. I would like us to develop and for the government to stop spending money it does not have."