Wilhelm studied in Rostock. When he became duke, he tried to acquire more power, which gave rise to a conflict with the local nobility. Wilhelm took part in the struggle against the Swedish landing near Riga. In 1609 in Königsberg he married the daughter of the Duke of Prussia, Sophie, but this happy marriage was interrupted by the early death of his wife. The conflict with the nobility became aggravated and in 1615 the nobles accused Wilhelm of having organized a murder. In 1616 Wilhelm lost the throne and went into exile; in 1632 he recovered the title of duke, but he was not allowed to return to Courland.
Wilhelm was buried in the vault on February 23, 1643. The massive pewter sarcophagus is richly decorated; there are the coats of arms of Courland and Prussia on each side of it and a crucifix on the lid. The gown is partly restored.