Made a treaty with Ottakar IV., duke of Styria, an arrangement which brought Styria and upper Austria to the Babenbergs in 1192, and in 1229 Duke Leopold II.
After the duke had three times refused to appear before the princes, Frederick placed him under the ban, declared the duchies of Austria and Styria to be vacant, and, aided by the king of Bohemia, the duke of Bavaria and other princes, invaded the country in 1236.
Bavaria was granted to Otto of Wittelsbach, but it lost some of its importance because Styria was taken from it and made into a separate duchy.
Four years after the fall of Ottakar he obtained from the princes a tardy and reluctant assent to the granting of Austria, Styria and Carniola to his own sons, Rudolph and Albert.
He died in October 1439, and was succeeded by his kinsman Frederick, duke of Styria, who became German king as Frederick IV.