Holownia announced his decision to take part in the next year's presidential race as the leader of Poland 2050 on November 13.
On Saturday, the PSL's Main Council announced they would also back his candidacy.
Poland 2050 and PSL earlier formed an alliance under the banner of the Third Way, for parliamentary, local and European elections.
PSL leader Wladyslaw Kosiniak-Kamysz said on Saturday that the PSL-Poland 2050 alliance in previous elections, especially last year's parliamentary elections, had a positive effect.
"Without this, we would not have won the elections which was extremely important," he added.
Kosiniak-Kamysz said that at the time "we also agreed on a certain election scenario, that we would start with the parliamentary elections and the finale would be the presidential elections".
He added that Holownia "deserves to be given a chance, to be supported and helped" but that Holownia's vision "of course has to be the vision of Poland that we support."
Holownia told PSL's Main Council that "the salvation for Poland is diversity and multi-centrism so that the next presidency will not be a constant arena of war between two political camps taking a large part of Poles hostage".
"The president must be someone who will be able to unite the nation in the face of great challenges, and at the same time be a challenge to the government, not to throw obstacles in its way, veto everything or sign everything," Holownia said referring to the incumbent President Andrzej Duda.
Following Holownia's statement, PSL Main Council accepted by acclamation the motion to support his candidacy.
"The Main Council of PSL, and through this the whole party, will support this candidacy, will support the campaign, we will actively engage in all activities that are needed to unite Poland and Poles," Kosiniak-Kamysz declared later at a press conference.
Holownia ran for the Polish president in the previous elections in 2020. In the first round, he won almost 14 percent of the votes, placing third after the incumbent Andrzej Duda and the Warsaw Mayor Rafal Trzaskowski, who is a presidential candidate of the governing centrist Civic Coalition.
The presidential ballot will be held in May 2025. Poles will elect their next president for a five-year term.(PAP)
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