The invasion of the Imperial troops in Brzeg (1633), forced the escape of John Christian and his morganatic family to Poland.

In 1635, Emperor Ferdinand II entrusted George III the administration of Brzeg during the absence of his father, who never returned home.

After the death of their uncle George Rudolf in 1653, the brothers inherited Legnica and Wołów; however, only one year later (1654), they decided to make a formal division of their domains: George III retained Brzeg, Louis IV obtained Legnica and Christian received the small towns of Oława and Wołów.

When his brother Louis IV died without surviving issue in 1663, George III and Christian inherited Legnica together as co-rulers.

In Bierutów on 23 February 1638, George III married firstly with Sophie Katharina (b. Oleśnica, 2 September 1601 – d. Brzeg, 21 March 1659), daughter of Charles II, Duke of Ziębice-Oleśnica by his wife Elisabeth Magdalena of Brieg, sister of George III's grandfather Joachim Frederick; thus, she was his first cousin once removed.