Born in Baden-Baden, he was the eldest son of Margrave Edward Fortunatus of Baden and Maria of Eicken.

Wilhelm only received the Regency of Baden after the victory of Johann Tserclaes, Count of Tilly in the Battle of Wimpfen over Georg Friedrich, Margrave of Baden-Durlach, whose brother Ernst Friedrich had occupied Baden-Baden in 1594.

Between 1626 and 1631, some 244 people, mostly women, were charged and 231 were condemned and burned in the Baden-Baden witch trials.

During this fighting, Wilhelm was taken prisoner, but not recognized and released as an ordinary soldier.

First marriage: Wilhelm married on 13 October 1624 Princess Catherine Ursula of Hohenzollern-Hechingen (died 2 June 1640), daughter of Count John George of Hohenzollern-Hechingen.