Little is known of his early life. He was born to a peasant family some time between 1525 and 1530 in the town of Goniądz. According to Symon Budny his true name was "Giezek", though throughout his life he used a variety of names and pseudonyms, including Gonesius, Gonedzius, Conyza and Koniński. He was sent by his parents to a monastery and became a priest. Supported by the bishop of Wilno Paweł Holszański, Piotr was sent to Italy, where he graduated from the University of Padua. There he received a doctorate in philosophy and became one of the professors. However, following his lecture of the anonymous work by Miguel Serveto and similar works by an Italian professor Matteo Gribaldi, Piotr of Goniądz converted to Protestantism and returned to Poland.