Duchy of Jawor
Although John had not been ordained as a priest, Matthias Corvinus obtained a dispensation from Pope Sixtus IV, allowing him to appoint John as bishop of Várad in 1476. John was consecrated as bishop on 23 May 1477. After his appointment as bishop, John still worked for Matthias, who appointed him as Chancellor in 1478. Later that year, John tried to reconcile between Matthias and the Utraquist Estates. In 1380, he mediated in a conflict between King Vladislaus II of Bohemia and the Utraquist citizens of Prague. In 1481, Matthias appointed him governor of the Duchy of Jawor.