His mother, a daughter of Bazyli Ustrzycki, castellan of Przemyśl, was the widow of Prince Antoni Lubomirski.

His father was Deputy Chamberlain of Lithuania (1742–1773), Commander of the Royal Army and a knight of the prestigious Order of the White Eagle, awarded on August 3, 1744 in Warsaw.

His father was the brother of the last King of Poland and Grand Duke of Lithuania, Stanisław II Augustus, who saw in his nephew a possible successor and heir to the throne of the Polish–Lithuanian Commonwealth.

Very well educated and particularly interested in the finances and economy of the country as well as in the arts, Poniatowski was not popular amongst szlachta (the Polish nobility), who found him arrogant and competitive.

Poniatowski commissioned about 2500 engraved gems from a group of gem-engravers in Rome who turned to classical literature for inspiration.