After completing his studies, he became and advisor and treasurer to Emperor Charles V and fought in the Battle of Pavia in 1525.
His post required that he provide horses and knights to Duke Louis X of Bavaria and to the Emperor to fight the war against the Ottoman Empire.
George's brother, Christopher of Leuchtenberg (d. 1554) commanded the cavalry in the army of Albert II Alcibiades.
Christopher and Albert took several loans from George and the latter was cited before the Reichskammergericht for breach of the peace.
George III married on 29 September 1527 at the Plassenburg with Barbara of Brandenburg-Ansbach-Kulmbach, daughter of Margrave Frederick I of Brandenburg-Ansbach.