French nobleman, soldier, and statesman who, as premier of France (1815–18 and 1820–21), obtained the withdrawal of the Allied occupation army from France. Earlier, he had served Russia as governor of Odessa and was notable for his progressive administration there.

The son of Louis-Antoine-Armand du Plessis, duc de Fronsac, and grandson of Louis-François-Armand de Vignerot du Plessis, duc de Richelieu and marshal of France, Armand took over his grandfather's duties at court as first gentleman of the bedchamber (1785). On a visit to Germany and Austria in 1790 he joined the Russian army, fighting against the Turks at Izmail, and then visited Russia. Succeeding his father as duc de Richelieu (1791), he fought with the royalists under the Prince de Condé (1792) and with the Austrians (1793–94). Visiting Russia in 1795, Richelieu was appointed lieutenant colonel of the Cuirassiers of St. George, and later Tsar Alexander I appointed him governor of Odessa (1803) and governor general of New Russia, the area between the Dniester River and the Caucasus (1805). After cleaning up a corrupt administration, Richelieu transformed the Black Sea village of Odessa into a modern city. He constructed port facilities and encouraged agriculture and commerce.

Richelieu returned to France in 1814, but on Napoleon's return from Elba in 1815 he joined the Tsar's forces against Napoleon. He succeeded Talleyrand as prime minister with control of foreign affairs in September 1815. His friendship with the Tsar helped him to mitigate the demands of the Allies on France, and at the Congress of Aix-la-Chapelle (Aix-la-Chapelle, Congress of) (1818) he obtained the withdrawal of the Allied occupying army and the inclusion of France into the Quadruple Alliance. He resigned in 1818, became prime minister again in 1820, but was forced by political opponents to resign again in 1821.