Both opposition parties, the liberal Civic Platform (PO) and the Social Democrats (SLD), also want early polls so a motion to dissolve parliament was expected to be approved easily.
The PiS and the PO between them have 61 per cent of the seats in the Sejm, Poland's lower house.
The prime minister met his twin brother, Lech Kaczynsk, the Polish president, and Donald Tusk, the liberal opposition leader, before the announcement.
Poland's latest crisis erupted in early July, when the prime minister sacked Andrzej Lepper, the deputy prime minister and leader of the populist Self-Defence (Samoobrona) party, over corruption allegations.
Samoobrona responded by saying it was leaving the coalition.
Lepper has denied the charges against him and has threatened to level unspecified allegations of wrongdoing against the prime minister.
President Kaczynski and Tusk agreed on Thursday that it was "inevitable" that elections scheduled for 2009 would have to be brought forward, most probably to October.
Tusk said it was time to end the "mounting chaos".
Kaczynski's party narrowly defeated the PO in the last election in 2005, but turnout was extremely low with less than 40 per cent of voters bothering to cast ballots.
However, Kaczynski failed to stand by an election promise to form a coalition with the liberal Civic Platform, opting instead for a minority cabinet before seeking an alliance with the populist Self-Defence (Samoobrona) party and the right-wing Catholic League of Polish Families.
Squabbling between the PiS and its junior partners led to a drop in support in opinion polls despite a flourishing economy with a six per cent growth rate and a sharp plunge of Poland's unemployment rate.