One of the pioneers of anabaptism in Poland, he was active as one of the notable members of the Protestant community formed around Mikołaj Radziwiłł. It was he who contacted the anabaptists exiled from the German states who settled in large numbers in Moravia and convinced many of them to settle in Poland. He was also heavily influenced by the views of Bohemian Hussites, who supported modesty, life in poverty and disregard for mundane life. For his support of unitarianism and anti-trinitarianism at the Protestant council of Secemin (22 January 1556), he was officially excommunicated at the council of Pińczów in April of that year. He was also banished from Lesser Poland. However, he found several supporters of his ideas, mostly from among the lesser szlachta of Podlaskie and the lands of Grand Duchy of Lithuania. Probably in 1558 he found a benefactor and patron in person of Jan Kiszka, one of the most powerful magnates of his time. Invited to Węgrów, Piotr became the head of the local Protestant commune and one of the most notable leaders of the Calvinist community in Poland.