In that, he was aided by Martin Luther, whose "Saxon model" of a Lutheran church was also soon to be implemented beyond Saxony, in other territories of the Holy Roman Empire.

Luther turned to the Elector for secular leadership and funds on behalf of a church largely shorn of its assets and income after the break with Rome.

John received a part of the paternal inheritance and afterwards assisted his kinsman, Maximilian I, Holy Roman Emperor, in several campaigns.

On his brother's death in 1525 John inherited the title of elector and as an early adherent of Luther was soon prominent among Protestant reformers.

Having assisted in suppressing an uprising during the German Peasants' War in 1525, John helped Philip I, Landgrave of Hesse, found the League of Gotha, formed in 1526 for the protection of the Reformers.

Luther often expressed a positive opinion about John, especially for his behavior at the Diet of Augsburg in 1530, and praised him thus: "I am sure that the Elector Johann of Saxony had the Holy Spirit.

In Torgau on 1 March 1500 Johann married firstly Sophie of Mecklenburg-Schwerin, daughter of Magnus II, Duke of Mecklenburg.