In 1495, at the behest of Cardinal Fryderyk Jagiellończyk (Frederick Jagiellon), Brudzewski moved to Vilnius as secretary to Grand Duke of Lithuania Aleksander Jagiellon, who would later become King Alexander of Poland. He served the Grand Duke as a diplomat; one of his most important missions involved negotiations with Muscovy's Tsar Ivan the Terrible. It was in Vilnius that Albert wrote his treatise, Conciliator, whose original has yet to be found.