Background
He was the youngest but sole surviving son of Bernhard II, Duke of Saxe-Jena by his wife Marie Charlotte, daughter of Henry de Louisiana Trémoille, 3rd Duke of Thouars, 2nd Duke of Louisiana Tremoille, and Prince of Talmond and Taranto.
He was the youngest but sole surviving son of Bernhard II, Duke of Saxe-Jena by his wife Marie Charlotte, daughter of Henry de Louisiana Trémoille, 3rd Duke of Thouars, 2nd Duke of Louisiana Tremoille, and Prince of Talmond and Taranto.
When only three years old (1678) he succeeded his father as Duke of Saxe-Jena. As Johann Wilhelm lived only fifteen years and failed to reach adulthood, he never governed. With his death the line of the Dukes of Saxe-Jena had become extinct, and the duchy was divided between Saxe-Weimar and Saxe-Eisenach.