He received an excellent education under the supervision of Dietrich von Bulow, Bishop of Lebus and Chancellor of Frankfurt University.
Joachim became elector of Brandenburg on his father's death in January 1499. He took some part in the political complications of the Scandinavian kingdoms, but the early years of his reign were mainly spent in the administration of his electorate, where by stern and cruel measures he succeeded in restoring some degree of order.
On the approach of the imperial election of 1519, Joachim's vote was eagerly solicited by the partisans of Francis I, king of France, and by those of Charles, afterwards the emperor Charles V. Having treated with, and received lavish promises from, both parties, he appears to have hoped for the dignity for himself; but when the election came he turned to the winning side and voted for Charles. In spite of this step, however, the relations between the emperor and the elector were not friendly, and during the next few years Joachim was frequently in communication with the enemies of Charles.
He was among those who met at Dessau in July 1325, and was a member of the league established at Halle in November 1533.
He died at Stendal on the 11th of July 1535.
Joachim is best known as a pugnacious adherent of Catholic orthodoxy.
After 1499 he married Elizabeth, daughter of John, king of Denmark.
His wife adopted the reformed faith, and in 1528 fled for safety to Saxony; and he had the mortification of seeing these doctrines also favoured by other members of his family.