Born in Cölln on the Spree (today part of Berlin), George William was the son of John Sigismund, Elector of Brandenburg and Anna of Prussia.

[1] In 1619, George William inherited the Margravate of Brandenburg and the Duchy of Prussia, then a vassal of the Polish–Lithuanian Commonwealth, although his ownership was not confirmed by Sigismund III Vasa until September 1621.

He proved a weak and ineffective ruler in a very difficult period of history; possession of Prussia involved him in the 1621 to 1625 Polish–Swedish War, since Gustavus Adolphus of Sweden was married to his sister Maria Eleonora.

[2] During the Thirty Years' War, the Calvinist George William tried to remain neutral in the contest between the Catholic Emperor Ferdinand II, and his mostly Lutheran opponents.

[4] Leaving his Catholic and pro-Imperial chief minister Schwarzenberg to run the government, George William withdrew in 1637 to the relatively untouched region of Prussia, where he lived in retirement until his death at Königsberg in 1640.