The Duchy of Courland and Semigallia had been created in 1561 by Gotthard Kettler, last master of the Livonian Order, and had been ruled by his descendants until the dynasty died out in 1737.

Finally, under pressure from Saxony and Poland, to sort out the selection of a new duke, the local nobility chose in 1758 their favoured candidate, the son of the Polish king, Prince Charles Christian.

Thereupon Charles, who had signed only a rather vague assurance about religious observance and aristocratic privileges, travelled to Courland and, on 29 March 1759, solemnly entered the capital of his Duchy, Mitau.

In July 1762, Catherine — who had disapproved of Duke Charles because of his apparent lack of interest in the welfare of his subjects — took the Russian throne in a coup d'état.

She allowed the now entirely rehabilitated von Biron to return from exile and put substantial diplomatic pressure on Saxony, with the aim of restoring him to his old position as Duke.

Finally, an ailing Augustus III — not only because of his declining health but also as a consequence of the Seven Years' War — accepted the fate of his son and denied him his support.

His hopes of regaining the Duchy of Courland evaporated after the shortly ensuing death of his father and the Saxon Electors' loss of the Polish Crown.

On 25 March 1760 in Warsaw, Charles had secretly married Countess Franciszka Krasińska, third daughter of Count Stanisław Korwin Krasiński (1717–1762) and his wife, Aniela Humięcka (b.