In the following years, he lived quietly in the Archduchy of Austria. After the outbreak of the Seven Years' War (1756–1763), in the spring of 1757, Joseph was appointed Commander of the Imperial Army, with orders to advance against King Frederick II of Prussia. Together with a French Corps, the Imperial Army was defeated in the Battle of Rossbach (5 November 1757). Joseph, shamed by the defeat, decided to renounce all military functions. In the evaluation by later historians the prince was nearly always blamed for the defeat, although he could hardly have changed the outcome of the fight, because of the catastrophic condition of the Imperial Army and the ineffectiveness of the French troops. Rather symbolic was the appointment to the post of "Field Marshal of the Imperial Army" (9 November 1785), with which the military career of Joseph ended. He died shortly after.