He was the first son of Anton Ulrich, Duke of Saxe-Meiningen and Charlotte Amalie of Hesse-Philippsthal.

August Friedrich succeeded his father in the duchy of Saxe-Meiningen (1763) when he was only eight years old.

Because of this, his mother, the Dowager Duchess Charlotte Amalie, acted as regent during his minority, which ended in 1779.

In Gedern on 5 June 1780, Karl Wilhelm married Louise of Stolberg-Gedern.

The widowed Louise later married Duke Eugen of Württemberg and had issue.