Prince William was the fourth and youngest son of King Frederick William II of Prussia and Princess Frederika Louisa of Hesse-Darmstadt. He served in the Guards from 1799 and fought in 1806 at the head of a cavalry brigade at Battle of Jena and Auerstedt. In December 1807, he traveled to Paris, to try to reduce the war burdens imposed on Prussia by Napoléon Bonaparte; he only managed to obtain a modest reduction. In 1808, he represented Prussia at the Congress of Erfurt. At the end of 1808, he accompanied his brother, King Frederick William III to St. Petersburg. Later, he had a prominent role in the transformation of Prussia and its army. During the War of the Sixth Coalition of 1813, he was stationed in Blücher's headquarters. In the Battle of Lützen on 2 May, he commanded the reserve cavalry in the left wing of the army and during the Battle of Leipzig, he negotiated the union of the Northern army with Blucher's. Later he led the 8th Brigade of the Yorck's army corps on the Rhine and distinguished himself by bravery and military skills at the battles of Château-Thierry, Laon and outside Paris. After the Treaty of Paris, the Prince accompanied the king to London and then attended the negotiations of the Congress of Vienna. In 1815 during the Waterloo Campaign he commanded the reserve cavalry of the Prussian IV Corps. After the second Treaty of Paris, he lived mostly in Paris and sometimes at his Fischbach Castle in Kowary in the Riesengebirge mountains. From 1824 to 1829 he was governor of the Confederate Fortress at Mainz; from 1830 to 1831 he was governor-general of the Rhine Province and Westphalia. In this capacity, on 20 September 1831 he opened the first rail line on German soil from Hinsbeck via the Deilbach valley to Nierenhof. Until then, the line had been called Deilthaler Eisenbahn ; after its opening it was allowed to call itself Prinz-Wilhelm-Eisenbahn-Gesellschaft. In March 1834 he was appointed general of cavalry and re-appointed as governor of the federal fortress at Mainz. He should not be confused with his nephew of the same name, the future emperor William I, who was governor of the same fortress in 1854. After the death of his wife, Marie Anna, on 14 April 1846, he withdrew from public life at his Fischbach castle.
