In 1368 he was appointed as provost of Vysehrad, and was late canon in the same see. In 1380-1387 he was bishop of Litomyšl (in this period, he was excommunicated in a dispute with the archbishop of Prague), then bishop of Olomouc until 1388, when pope Urban IV named his as feudal patriarch of Aquileia. Once in Friuli, he had to face a critical situation in which most of the feudal families of the patriarchate had seized local power for themselves.
The events precipitated when the patriarch"s marshal murdered the noble Federico Savorgnan at Udine, causing a popular rebellion which was supported by the Republic of Venice.
The patriarch took refuge in the castle of Soffumbergo. However, John was lured to Udine for a fake negotiation, and he was assassinated there by Tristano Savorgnan, Federico"s son (13 October 1394).
He was secretly buried in the Cathedral of Udine to avoid further upheavals.