He was the second son (but fourth in order of birth) of the eight children of Frederick II, Elector of Saxony and Margarete of Austria, sister of Frederick III, Holy Roman Emperor.
The death of his older brother Frederick (1451) made him the new heir apparent to the position of Elector of Saxony.
In 1455 Ernst was kidnapped along with his brother Albert, an episode famous in German history as the "Prinzenraub" (i. e. The Stealing of the Princes).
In 1464, he succeeded his father as Elector of Saxony, and annexed Thuringia in 1482, and three years later (Treaty of Leipzig, 1485) shared his territory with his brother Albert, until he arranged the division of the common possession.
In the Division of Leipzig he received area around Wittenberg, the south Thuringian part, the Vogtland and parts of the Pleissnerland. As residence he selected Wittenberg. He provided for the welfare of the country and introduced the constitution.
One year after the division elector Ernest died in Colditz, at the age of 46 years, the consequence of a fall off a horse.
In Leipzig on 19 November 1460 Ernst married with Elisabeth of Bavaria-Munich. They had seven children: