Wincenty Witos, a leader of the Polish People's Party (PSL) who was prime minister three times between the wars, and the others, all of whom belonged to opposition parties, were convicted in the infamous Brest Trial, which lasted from October 26, 1931, to January 13, 1932.
The men went on trial accused of a planning a coup d'état against the Polish government, then led by Marshal Jozef Pilsudski. Their trial, and subsequent conviction, was seen as part of an increasingly repressive policy orchestrated by the Pilsudski government designed to silence political opposition.
Michal Laskowski, the president of the Criminal Chamber said that the original investigation and trial "constituted an example of the instrumental use of the law and the court to persecute political opponents".
He added: "It was an example of an abuse of law that is unacceptable."
Wladyslaw Kosiniak-Kamysz, the current PSL leader, welcomed the Supreme Court's decision, calling it a "historic moment" that "wiped away the disgrace of the Brest Trial." (PAP)