When the War of the Third Coalition broke out, Weyrother was promoted to "Generalmajor" (major general). After the death of the Allied army chief of staff, Johann Heinrich von Schmitt at the Battle of Dürenstein on 11 November 1805, the Allied commander-in-chief, the Russian General Mikhail Kutusov requested that Weyrother be made chief of staff of the Austro-Russian army. Although the two men soon fell out, as Kutuzov wanted a defensive strategy, Weyrother gained the favour of Tsar Alexander I of Russia with his aggressive strategy. With the Tsar's support, he created the plan for the Battle of Austerlitz in which the Allies were crushed by Napoleon on 2 December 1805. The defeat was so bad, the Russians accused Weyrother of being in the pay of the French. Weyrother withdrew from military life and retired to Vienna, where he died aged 51.