Augustus's eldest surviving son, Frederick Christian of Saxony, succeeded his father as Elector but died two and a half months later. In the Commonwealth, on September 7, 1764, with the small participation of the szlachta initiated by the Czartoryski's and the strong support of Russia, Stanisław August Poniatowski was elected king of Poland and Grand Duke of Lithuania.
John's older brother became King Frederick Augustus II in 1836; now he was the first in line of succession to the throne. The King, married twice, was childless. John remained as heir presumptive during all the reign of his brother. King of Saxony. John became King of Saxony after the death of his brother Frederick Augustus II on 9 August 1854.