European Union leader Donald Tusk announced that he won't run to be the president of his native Poland, saying he carries too much "baggage" from his time as prime minister.
The exit poll, conducted by the research firm Ipsos, projected that Law and Justice won 43.6% of the votes.
Concerns about democracy have made this one of the country's most momentous elections since the fall of communism 30 years ago.
Although European Council president Donald Tusk only appeared in court as a witness, some officials who served under him when he was prime minister of Poland in 2010 are being sued for not ensuring the safety of President Lech Kaczynski's plane.
Polish parliament to vote on a new government next Tuesday, and any ministerial changes are expected to be announced after that.
The investigation will focus on whether criminal charges should be brought for "public propagating of fascism" during march on Poland's Independence Day.
European Council President Donald Tusk says the questioning leave him in no doubt that he is a political target of the ruling Law and Justice party.
Polish President Andrzej Duda on Monday announced that he will veto two of three bills reforming the country's judiciary system.
Polish President Andrzej Duda made a surprise compromise bid over controversial court reforms that aim to expand the justice minister's powers as thousands of protesters took to the streets over the proposed changes.
Massive protests by thousands of women force Poland's right-wing dominated parliament to withdraw its support for plans to ban abortion.
Poland claims European Union's plan to distribute 120,000 refugees across EU member countries is not feasible
Jaroslaw Kaczynski blames European Council president Donald Tusk over Polish president's plane crash in 2010
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