The populist party swept into power in 2015, promising voters welfare reforms, social conservatism, and a bigger state role in the economy. The ruling right-wing Law and Justice party is hoping to strengthen its firm grip on power, which has been buoyed by handing out social benefits and questioning how much authority the European Union should have over member nations.
The party won some 32.3 per cent of votes for provincial assemblies, compared with 26.9 per cent in a vote four years earlier.
The Civic Coalition, an alliance between the Civic Platform (PO) and Nowoczesna (Modern) parties, came second with 24.7 percent of the regional assemblies vote, the poll found.
"This result bodes well for the parliamentary election", PiS leader Jaroslaw Kaczynski said after the exit poll was released.
The Ispos survey says that Rafal Trzaskowski, a former European lawmaker, garnered 51.4 percent support and will become Warsaw mayor without having to take part in a November 4 runoff. Final results are expected on Tuesday or Wednesday.
While exit poll results cannot give a clear indication of how many of Poland's 16 provincial assemblies will fall under PiS control, any gains will mean better access to local funding. That could affect a general election in 2019.
PiS leader Jarosław Kaczyński in Warsaw on Sunday.