George William was the eldest but only surviving son of Duke Christian of Legnica-Brzeg (1618–1672) by his wife Louise (1631–1680), a daughter of the Ascanian prince John Casimir of Anhalt-Dessau.

After his father's death in 1672, the then twelve-year-old George William succeeded him as Duke of Legnica and Brzeg; during his minority, the regency was exercised by his mother, Dowager Duchess Louise who held the towns of Wołów and Oława as her dower (wittum).

Fearing claims raised by the Habsburg Emperor Leopold I in his capacity as ruler over the Crown of Bohemia, Duke Christian had devised by will that his son was formally under the tutelage of his maternal uncle Prince John George II of Anhalt-Dessau and the mighty Hohenzollern elector Frederick William of Brandenburg.

The day before his father's death, Louise sent her son to study at the Viadrina University in Brandenburgian Frankfurt/Oder, considered as an act of mistrust by the Imperial court.

Upon his death, the Duchy of Legnica-Brzeg reverted to Emperor Leopold as ruler over the Bohemian crown lands, which since 1526 were integral part of the Austrian Habsburg monarchy.

Leopold took up the government by a Landeshauptmann deputy, despite the claims of George William's morganatic uncle Count August of Legnica, and had several Counter-Reformation measures implemented.