He was the second son of Landgrave Louis VIII and Charlotte Christine Magdalene Johanna of Hanau-Lichtenberg.

He was the official military adviser to his father, but had a strong rival in his older brother Louis IX, who followed the example of his friend the soldier-king Frederick II of Prussia and expanded Pirmasens as a garrison town.

Through this marriage, he acquired the estates of Broich, Oberstein, Aspermont, Burgel, and Reipolzkirchen.

In 1764, George William received Old Palace in Darmstadt and the associated pleasure garden as a gift from his father, who had always favoured him above his brother Louis.

[citation needed] George William had the palace with the White Tower expanded.