Their educational tour began at the end of August 1613; the brothers visited France, Great Britain and the Netherlands before returning home in 1614.

In 1620 Wilhelm became regent of all the estates of his older brother, Johann Ernst, after the latter was subject to the ban of the Empire for refusing to submit to the emperor.

Wilhelm allied himself with his brothers in the Thirty Years' War, serving under Ernst von Mansfeld and Georg Friedrich, Margrave of Baden-Durlach.

During the division of the paternal states in 1640, Wilhelm retained Weimar and Jena, and his younger brother Albrecht received Eisenach.

They had nine children:[citation needed] Wilhelm wrote the words for the hymn Herr Jesu Christ, dich zu uns wend in 1648.