Career
He was a titular Duke of Saxony from the Ernestine branch of the House of Wettin. Due to neglect during his childhood, he was always sickly and weak. He had been interested in theology from a young age, and studied theology at the University of Jena.
After his father"s death in 1554, he received Saxe-Gotha as an apanage.
From 1557, he was allowed to rule Saxe-Gotha alone. In 1561, this contract was extended for another four years.
John Frederick III died unmarried and childless in 1565, at the age of 27. He was buried in the City Church in Weimar.