The confederacy sends an official delegation to Poland, headed by Johannes von Baysen, on February 10, 1454.

The delegates, in Kraków by February 20, have asked Casimir to bring Prussia into the Polish kingdom.

After negotiating the exact conditions of incorporation, the king agrees and delegates of the Prussian Confederation pledge allegiance to Casimir on March 6, 1454.

On the same day, the king agrees to all the conditions of the Prussian delegates—for instance, Thorn has demanded the destruction of the Polish city of Nieszawa—giving wide privileges to the Prussian cities and nobility.

Three days later, Johannes von Baysen is named as the first governor of Prussia.

Casimir marries Elisabeth of Austria, daughter of the late King of the Romans Albert II of Habsburg by his late wife Elisabeth of Bohemia, on March 10.

Her distant relative Frederick of Habsburg, who became Holy Roman Emperor in 1452, will reign as Frederick III until after Casimir's own death.

The marriage strengthens the ties between the house of Jagiello and the sovereigns of Hungary-Bohemia and puts Casimir at odds with the Holy Roman Emperor through internal Habsburg rivalry.

Elisabeth's brother is King Ladislaus the Posthumous.