Shortly before his birth his father, Jan Oleśnicki, was dispatched by king Władysław Jagiełło to serve as captain of Vilnius and to bring a detachment of knights there.

At the beginning of the Lithuanian Civil War the city was under the governance of the Polish king's brother, Skirgaila, and came under siege by the combined forces of the pagan Samogitians under Jagiello's cousin and rival Vytautas and the army of the Teutonic Order with their guest crusaders from France, England, and the Holy Roman Empire.

As cardinal, his influence in Poland was second only to that of the king, and, during the frequent absence of Casimir IV in Lithuania, he transacted the affairs of the State.

[6] In his conduct of Poland's affairs Oleśnicki entertained far-reaching imperial dreams, which included a complete assimilation of Lithuania into the Polish state and the conquest of Silesia from the Kingdom of Bohemia.

In particular, Oleśnicki pursued the idea of a Crusading alliance with Hungary against the Ottoman Turks, with the ultimate aim of extending Poland's boundaries to the Black Sea.

[citation needed] Being a man of great learning, he advanced the study of arts and letters in every possible way, and the flourishing condition of the University of Krakow during his episcopacy is due chiefly to his efforts.