He was the third but second surviving son of Frederick III, Duke of Saxe-Gotha-Altenburg and Luise Dorothea of Saxe-Meiningen.

In 1768 and 1769, both princes went on an educational journey to the Netherlands, England and France, and Ernest met important people in politics, science and the arts.

[1] For his special interests, he employed the services of the important astronomer Franz Xaver von Zach for Gotha.

In 1783, he became a member of the Bavarian Illuminati under the name of Quintus Severus and/or Timoleon, and in 1784, he was made Supervisor of Abessinien (a name for Upper Saxony).

In Meiningen on 21 March 1769, Ernest married Princess Charlotte of Saxe-Meiningen, the half-first cousin of his mother.