Officier de cavalerie originaire de la noblesse picarde, Armand de Caulaincourt (1773-1827) gravit rapidement tous les échelons de la cour consulaire puis impériale, devenant en 1804 grand-écuyer de l’Empire. Mais, malgré l’importance de ses fonctions curiales, Napoléon le destine à une carrière de diplomate. Après différentes missions, il le nomme ambassadeur de France en Russie, à la fin de l’année 1807. Fervent partisan de l’alliance de Tilsit, Caulaincourt participe à toutes les grandes négociations franco-russes mais doit assister à la lente dégradation des relations entre les deux empires. À son retour à Paris en 1811, son bilan politique est maigre. Sa défense opiniâtre du tsar Alexandre, mais surtout son opposition à la campagne militaire qui se prépare, irritent Napoléon. Elles lui permettent toutefois d’acquérir une nouvelle stature après le désastre de Russie : pour ses contemporains Caulaincourt devient l’« homme de la paix ». Une image que Napoléon réutilise lorsqu’il le charge de le représenter aux congrès de Prague (1813) et de Châtillon (1814). Le duc de Vicence, devenu ministre des Relations extérieures, ne parvient pas à faire accepter la paix ; il lui faut finalement négocier l’abdication de Napoléon et renoncer, après les Cent-Jours, à toute carrière politique. Cette étude, qui s’appuie sur les archives personnelles de Caulaincourt et ses célèbres Mémoires, entend redonner toute son importance à cette figure majeure du Premier Empire, en insistant sur son action et sa pensée dans le domaine de la diplomatie. L’exemple de ce parcours devant permettre de contribuer à reconsidérer et réévaluer le rôle du personnel diplomatique napoléonien. / A cavalry officer born into Picardy's landed gentry, Armand de Caulaincourt rose rapidly through the ranks of the consular, and later the imperial court, to become in 1804 Grand Squire of the Empire. However, notwithstanding the importance of his curial functions, Napoleon destined him to a diplomatic career. After several missions, he was appointed as Ambassador of France to Russia (1807). Caulaincourt took part in all the major negotiations between France and Russia, but was forced to witness a slow breakdown in relations between the two Empires. At the time of his return to Paris in 1811, his political accomplishments were unimpressive. His stalwart defense of Tsar Alexander, and especially his opposition to the upcoming military campaign, were an irritation to Napoleon. Nevertheless, these stances allowed him to gain new stature after the disaster in Russia : in the eyes of his contemporaries, he became the “Peacemaker”, an image Napoleon used to his advantage by appointing him his representative at the congresses in Prague (1813) and in Châtillon (1814). The Duke of Vicenza, now Minister for Foreign Affairs, could not, however, broker an agreement in favour of peace : he was forced to negotiate Napoleon's abdication and to give up any hope of political career after the Hundred Days. This study, based on Caulaincourt's personal records and famous Memoirs, aims at restoring a major figure of the First French Empire to his due importance, while focusing on his action and thought in the field of diplomacy. The exemplary value of his career should also allow historians to reconsider and reevaluate the role of Napoleon's diplomatic personnel.