In 1379 Jan, while yet a teenager, was named a provost of the Spiš Chapterhouse (in northern Hungary, then pawned to Poland), giving him substantial revenues.

[citation needed] In 1388, the death of Archbishop Bodzanta gave Jan the opportunity to obtain a more politically and important position; the Archbishopric of Gniezno.

In 1399 Jan returned to Poland, but in Kalisz he was stopped by partisans of King Władysław II, who forced him to take the oath of loyalty.

This conflict made ruling almost impossible for Jan. As a result, he became increasingly willing to cooperate with Poland; this was particularly revealed in 1410 during the Polish–Lithuanian–Teutonic War, when thanks to the mediation of Bishop of Gdańsk, he paid homage to the Polish king.

Jan's decision to remain on the Polish side had serious consequences for him: in 1411 he was imprisoned by the citizens of Wrocław, who were subjects of the Bohemian Kingdom and in this way could neutralize the bishop's activities.

Jan regained his freedom after three months through the personal intervention of Sigismund of Luxembourg, King of Hungary and Holy Roman Emperor.

In general, the relationship between Jan and the House of Luxembourg was good, and thanks to this, the Bishop obtained the Abbeys of Szekszárd and Pannonhalma (both in Hungary) as new revenues.

[2] During 1415-1417 Jan took part in the Council of Constance, which ended the so-called "Three-Popes Controversy" and therefore the Western Schism of the Roman Catholic Church.

Importantly for Jan personally, during the council the Teutonic Order guaranteed the inviolability of the Bishopric of Gdańsk Pomerania, thanks to the influence of the Curia and the support of the Polish delegation.