He was born in Gotha, the eldest son of Frederick II, Duke of Saxe-Gotha-Altenburg and Magdalene Augusta of Anhalt-Zerbst.

In 1734 he began a flourishing soldier trade with the Emperor, to the Prince of Waldeck and to the King of Prussia, which put him into the position to create a tax in his own duchy.

In Gotha on 17 September 1729, Frederick married Luise Dorothea of Saxe-Meiningen, his first cousin.

They had nine children: From 1748 to 1755 he was regent of the duchy of Saxe-Weimar-Eisenach on behalf of Ernst August II Konstantin.

From 1750, he acted as regent alongside his kinsmen Franz Josias, Duke of Saxe-Coburg-Saalfeld.