Jan fought in the Ottoman wars and participated in 1526 with Moravian troops on the Battle of Mohács, where King Louis II of Hungary was killed.

Pernštejn Castle, which his father had neglected, was rebuilt and expanded during Jan's reign and remodeled as a representative palace.

A treaty to that effect had been concluded before Casimir II's death and they had also decided that Jan's daughter Marie would later marry Wenceslaus III Adam, which she did in 1540.

In a secret addendum to this treaty, they had arranged that if ever Casimir's family would die out in the male line, then the Duchy of Teschen would fall to Jan or his descendants.

Since Jan, unlike Ferdinand, sympathized with the Reformation, he supported spread of Lutheranism and Utraquism in territory of Kladsko Land.

Although he supported the 1547 Bohemian uprising, the Estates of Kladsko did not participate in the rebellion and consequently, his county was spared when the King punished the rebellious areas.

As early as 1546, two years before Jan's death, his sons were started negotiations with Ernest of Bavaria, the administrator of Salzburg, about the possibility of selling the County of Kladsko to him.

A dispute arose when Jan's son Vratislav refused to sell him the Lordship of Hummel, western part of the Kladsko area.

When Ernest threatened to call off the whole transaction, Vratislav gave in and handed him Hummel, including the towns of Duszniki Zdrój and Lewin Kłodzki.

They had the following children: John married in 1544 with Magdalena Székely of Ormozd (d. 1556), a widow of the Hungarian magnate Alexei Thurzó of Bethlenfalva.