His father's testament, stipulated that Frederick should rule the Margraviate of Brandenburg jointly with his older brother Frederick Irontooth, who also acted as his guardian from 1440 onwards, until at least 1456.
In 1447, Frederick received his own territory, consisting of the Altmark and Prignitz, under the sovereignty of Electoral Brandenburg.
He fostered the influx of Jews into his territory, after his brother had driven them out of his margraviate in 1446.
He neglected the business of government in such a way that his brother found it necessary in 1459 to intervene militarily against the intrigues in the country.
His remains were recovered and buried in Berlin [2] Frederick married on 9 February 1449 in Tangermünde to Agnes (1436–1512), a daughter of the Duke Barnim VIII of Pomerania, with whom he had one daughter: This article about a German margrave is a stub.