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

In the Battle of Grocka he was wounded and then spent some time in Altenburg to recover.

Later he resumed his military duties and fought in the War of the Austrian Succession in Silesia, Bohemia, Bavaria and the Rhine.

He lived with his family in Stadtroda, where shortly before his death he received a visit from King Frederick the Great of Prussia.

On 6 January 1752 at Roda (Stadtroda after 1925), Johann August married Louise Reuss of Schleiz, co-Countess of Limpurg-Gaildorf since 1734 [as her mother's only surviving child][1] (Staffelstein, 3 July 1726 – Stadtroda, 28 May 1773), widow of his younger brother Christian Wilhelm.