Biography. He was the eldest son of Frederick III, Landgrave of Thuringia, and Catherine of Henneberg.After the death of his uncle William I, Margrave of Meissen in 1407, he was made governor of the Margraviate of Meissen together with his brother William II as well as with his cousin Frederick IV (son of Balthasar), until their possessions were divided in 1410 and 1415.
In Weimar on 26 May 1555 John Frederick II married his first wife, Agnes of Hesse, Dowager Electress of Saxony. Six months later she suffered a miscarriage and died, on 4 November 1555. In Weimar on 12 June 1558 John Frederick II married his second wife, Countess Palatine Elisabeth of Simmern-Sponheim , daughter of the later (1559) Frederick III, Elector Palatine .
From his birth, it was clear that one day Frederick Augustus would become the ruler of Saxony. His father was the only son of the Elector Frederick Christian of Saxony who left surviving male issue. When the King Frederick Augustus I died (1827) and Anton succeeded him as King, Frederick Augustus became second in line to the throne, preceded only by his father Maximilian.