From there, he went to the German frontier town of Coblenz and joined the counter-revolutionary émigré army of Louis XVI's cousin, the Prince of Condé.

While in the pay of Austria, he then travelled to Warsaw and rejoined the court-in-exile of the pretender to the throne of France, King Louis XVI's younger brother, the Comte de Provence, who charged him with various missions, including one to Saint Petersburg.

In 1809, Blacas was made the pretender's grandmaster of the wardrobe (grand-maître de la Garde-Robe du Roi).

A scapegoat for the royalist excesses of 1814, Blacas was unofficially exiled as the French ambassador to the court of the Kingdom of Two Sicilies, whose capital was located in Naples.

There, he negotiated the 1816 marriage of the Louis XVIII's nephew, the Duke of Berry, to Francis I of the Two Sicilies's daughter Caroline.

Remaining in Rome for many years, he provided the French artist Jean Auguste Dominique Ingres in 1817 with his first official commission since 1814 and became a patron to the German classicist Theodor Panofka, who returned with him to Paris in 1828.

Blacas was also appointed superintendent to the Crown properties (intendant général des Bâtiments de la Couronne).

He died on 17 November 1839 and was buried next to the Bourbon crypt of the Kostanjevica Monastery in Görz, Austria, now on the Slovenian side of the border in Nova Gorica.