The state electoral commission said Monday Law and Justice won 43.59% of Sunday's vote, which translates into 235 of the 460 seats in the Sejm. That's the same number of seats the party won in 2015. It currently holds 240 seats following a migration of lawmakers to Law and Justice.
Poland's main opposition Civic Coalition won 27.4% of votes, or 134 seats. The coalition is a centrist alliance built around the Civic Platform party, once led by European Union leader Donald Tusk. Voters returned left-wing parties to parliament after a four-year absence. A group led by the Democratic Left Alliance won 49 seats with 12.56% of the vote.
Thirty seats are going to the agrarian Polish People's Party and 11 seats to Confederation, a new far-right group.
Officials from Poland's ruling party say Prime Minister Mateusz Morawiecki is a "natural" to stay on as head of government after the party's second consecutive election victory.
Government spokesman Piotr Mueller said Monday it would take up to three weeks to form and swear in a new government.
Mueller says Law and Justice party leader Jaroslaw Kaczynski has repeatedly praised Morawiecki and said he would continue in the job after Sunday's election.
Law and Justice deputy leader Joachim Brudzinski called Morawiecki an "excellent prime minister who has had undeniable successes."
President Andrzej Duda needs to give a candidate proposed by the winning party a mandate to form a government.
Official returns from 99.5% percent of the votes counted in Poland's parliamentary election suggest the country's ruling right-wing party might have lost its majority in the upper chamber, the Senate.
According to the State Electoral Commission on Monday, the Law and Justice party won just under 45% of votes Sunday for the 100-seat Senate, which translates to 49 senators, down from the 61 senators it now has. Opposition parties seem to have won 51 seats.
Returns from voting abroad still need to be counted, but they are not expected to change the breakdown of the seats.
Law and Justice Sen. Jan Maria Jackowski said Monday the party has found itself in a "new situation" in the Senate that means it will have to negotiate more to pass laws.
The Senate has the power to block or amend proposed legislation that has been approved by the lower chamber.
The Organization for Security and Cooperation in Europe says "clear media bias as well as intolerant rhetoric" by politicians detracted from a weekend election in Poland that was otherwise well run.
The assessment from the OSCE, a democracy organization made up of 57 countries, came a day after Poles voted in an election to the 460-seat lower house of parliament and the 100-seat Senate.
Jan Petersen, the head of the election observation mission, said that there was high-level polarization in the public and private media. He said the ability of voters to "make an informed choice was undermined by a lack of impartiality in the media, especially the public broadcaster."
Under the ruling, the Law and Justice party, which won the election according to nearly complete results, used state media as a mouthpiece to praise its own and cast opponents in a negative light.
Petersen also said the discriminatory rhetoric used by "a number of leading political figures is of serious concern in a democratic society."
He did not give examples but the election took place in an extremely divided society. Recently the ruling party has used anti-gay rhetoric to shore up its conservative base.
Nearly complete results in Poland's weekend election confirm that the conservative ruling party Law and Justice capitalized on its popular social spending policies and social conservatism to do better than when it swept to power four years ago.
Poland's state electoral commission reported Monday that Law and Justice got nearly 45% of the vote, up from 38% in 2015.
Around 91% of the votes have been counted.
The results point to a Law and Justice majority in parliament.
The centrist Civic Coalition is running second with almost 27%, while a left-wing alliance is trailing with 12%. The conservative agrarian Polish People's Party got nearly 9%, while Confederation, a new far-right group that is openly anti-Semitic and homophobic, is set to enter parliament after winning 6.8% of the vote.