Prime Minister Donald Tusk has become the first Polish leader to be re-elected since the end of communism, according to BBC.
Officials results, announced after 93% of votes had been counted, gave Mr Tusk`s Civic Platform party enough seats to continue in coalition.
The centre-right Civic Platform took 39% of the vote, against 30% for its conservative challenger, the Law and Justice Party.
The leader of Law and Justice, Jaroslaw Kaczynski, has admitted defeat.
Civic Platform becomes the first Polish party to win two consecutive terms since communism`s fall in 1989.
Mr Tusk, 54, appears to have been rewarded for presiding over four years of strong economic growth, since winning a snap election in 2007.
Poland has been the only EU member state to avoid recession, and this year its economy is forecast to grow by about 4%, the highest rate among the EU`s seven largest economies.
The electoral commission said Civic Platform`s 39% would translate into 206 seats in the 460-member lower chamber.
Mr Tusk`s coalition ally, the People`s Party, won 8.6% of the vote, or 30 seats.
Law and Justice won 157 seats; a new liberal pro-secular party, Palikot`s Movement, came third with 10%, giving it 40 seats; the Democratic Left Alliance was the fifth party to make it into parliament, taking 8.2% and 26 seats.
Mr Tusk said he would work on forming a governing coalition on Monday.
He is expected to renew his alliance with his current partner, the agrarian-rooted People`s Party, which has said it is willing to team up with the Civic Platform again if an offer is made.
He campaigned on his economic success and also vowed to pursue a steady rapprochement with Russia, despite rows over missile defence and gas pipelines as well as the conduct of an inquiry into a plane crash that killed Poland`s president last year.
"It is the highest honour for me and for Civic Platform that we will be working for the next four years for all of you, regardless of who you voted for today," Mr Tusk told supporters on Sunday.
"In the next four years we will work twice as hard," he said, according to AP news agency.
The Law and Justice Party`s Jaroslaw Kaczynski is known for his mistrust of the two countries which invaded Poland during World War II, Germany and the USSR. He also attracts support from Polish Eurosceptics.
"I am deeply convinced that the day will come when we will succeed," Mr Kaczynski said. "Sooner or later we`ll win because we are simply in the right."
The 62-year-old served as prime minister from 2005 to 2007, with his twin brother, Lech, as president. Lech Kaczynski died in a plane crash with 95 others in April 2010.
Jaroslaw Kaczynski competed in the snap presidential polls which followed, but lost to Mr Tusk`s ally Bronislaw Komorowski.