<human>: Answer by taking a quote from the following article:

Francois-Rene (Auguste), vicomte de Chateaubriand (; French: [fRaswa R@ne d@ SatobRija]; September 4, 1768 - July 4, 1848), was a French writer, politician, diplomat and historian who is considered the founder of Romanticism in French literature. Descended from an old aristocratic family from Brittany, Chateaubriand was a royalist by political disposition; in an age when a number of intellectuals turned against the Church, he authored the Genie du christianisme in defense of the Catholic faith. His works include the autobiography Memoires d'Outre-Tombe ("Memoirs from Beyond the Grave", published posthumously in 1849-1850). In his early works, he used the name Auguste instead of Rene.

After the fall of the French Empire, Chateaubriand rallied to the Bourbons. On 30 March 1814, he wrote a pamphlet against Napoleon, titled De Buonaparte et des Bourbons, of which thousands of copies were published. He then followed Louis XVIII into exile to Ghent during the Hundred Days (March-July 1815), and was nominated ambassador to Sweden.  After Napoleon's defeat, Chateaubriand became peer of France and state minister (1815). In December 1815 he voted for Marshal Ney's execution. However, his criticism of King Louis XVIII in La Monarchie selon la Charte, after the Chambre introuvable was dissolved, got him disgraced. He lost his function of state minister, and joined the opposition, siding with the Ultra-royalist group supporting the future Charles X, and becoming one of the main writers of its mouthpiece, Le Conservateur.  Chateaubriand sided again with the Court after the murder of the Duc de Berry (1820), writing for the occasion the Memoires sur la vie et la mort du duc. He then served as ambassador to Prussia (1821) and the United Kingdom (1822), and even rose to the office of Minister of Foreign Affairs (28 December 1822 - 4 August 1824). A plenipotentiary to the Congress of Verona (1822), he decided in favor of the Quintuple Alliance's intervention in Spain during the Trienio Liberal, despite opposition from the Duke of Wellington. Although the move was considered a success, Chateaubriand was soon relieved of his office by Prime Minister Jean-Baptiste de Villele, the leader of the ultra-royalist group, on 5 June 1824.  Consequently, he moved towards the liberal opposition, both as a Peer and as a contributor to Journal des Debats (his articles there gave the signal of the paper's similar switch, which, however, was more moderate than Le National, directed by Adolphe Thiers and Armand Carrel). Opposing Villele, he became highly popular as a defender of press freedom and the cause of Greek independence. After Villele's downfall, Charles X appointed him ambassador to the Holy See in 1828, but he resigned upon the accession of the Prince de Polignac as premier (November 1829).  In 1830 he donated a monument to the French painter Nicolas Poussin in the church of "San Lorenzo in Lucina" in Rome. CANNOTANSWER

What other significance did he have during these years?
<bot>: After Napoleon's defeat, Chateaubriand became peer of France and state minister (1815).