The two parties signed a merger agreement, along with a 10-point 'ideological declaration' at a right-wing political convention in Przysucha, south-central Poland on Saturday.
In the declaration, they committed to work on a new constitution that would restore political order in Poland, an assertive policy towards the EU, "and in the case of going beyond the law and treaties - the defence of Polish sovereignty."
The signing follows an announcement by Jaroslaw Kaczynski, the leader of PiS, in September about his party's plan to absorb smaller parties that used to make up the United Right alliance ruling in Poland in 2015-2023, in which PiS was the dominant force.
During the Saturday event, Kaczynski said that "the opposition must begin the process of internal consolidation "to send a positive signal to the people that the Polish patriotic camp is uniting."
"And we have to look for alliances and allies only there, only in the Polish patriotic camp... this is our great task."
He argued that Poland currently faces very unusual challenges and that the alliance "is the only force that has the ability to defend Poland from all of that."
Patryk Jaki, Sovereign Poland's acting president, said the decision to join forces was driven by a desire to be "part of a concerted effort to fight for the country's future."
According to political commentators, PiS is seeking consolidation of the right-wing groupings ahead of the presidential election due in the spring of next year. The newly unified party is due to unveil its presidential candidate in November. (PAP)
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