In the year 1840 he entered the service of the French foreign office, and was appointed to a post under the marquis de la Valette, who was consul-general at Cairo. He spent eight years in Egypt, being appointed consul in 1845; in 1848 he was made consul at Palermo, and in 1851 he accompanied the marquis, who had been appointed ambassador at Constantinople, as first secretary.
For fifteen months during the progress of the Crimean War he acted as chargé d'affaires. In the second volume of his essays he gives some recollections of his experiences in the East, including an account of Mehemet Ali, and a (not very friendly) sketch of Lord Stratford de Redcliffe. In 1855, after refusing the post of minister at Teheran, he was employed in the foreign office at Paris, and acted as secretary to the congress at Paris (1855-1856). During the next few years he was chiefly occupied with Italian affairs, in which he was much interested, and Cavour said of him he was an Italian at heart. He was chosen in 1861 to be the first envoy of France to the king of Italy, but he resigned his post next year on the retirement of EA Thouvenel, who had been his patron, when the anti-Italian party began to gain, the ascendancy at Paris. In 1864 he was appointed ambassador at the court of Prussia.
Benedetti remained in Berlin till the outbreak of war in 1870, and during these years he played an important part in the diplomatic history of Europe. His position was a difficult one, for Napoleon III did not keep him fully informed as to the course of French policy. In 1866, during the critical weeks which followed the attempt of Napoleon to intervene between Prussia and Austria; he accompanied the Prussian headquarters in the advance on Vienna, and during a visit to Vienna he helped to arrange the preliIminaries of the armistice signed at Nikolsburg. It was after this that he was instructed to present to Bismarck French demands for "compensation," and in August, after his return to Berlin, as a result of his discussions with Bismarck a draft treaty was drawn up, in which Prussia promised France her support in the annexation of Belgium. This treaty was never concluded, but the draft, which was in Benedetti's handwriting, was kept by Bismarck and, in 1870, a few days after the outbreak of the war, was published by him in The Times. During 1867 Benedetti was much occupied with the affair of Luxemburg.
In July 1870, when the candidature of the prince of Hohenzollern for the throne of Spain became known, Benedetti was instructed by the duc de Gramont to present to the king of Prussia, who was then at Ems, the French demands, that the king should order the prince to withdraw, and afterwards that the king should promise that the candidature would never be renewed. This last demand Benedetti submitted to the king in an informal meeting on the promenade at Ems, and the misleading reports of the conversation which were circulated were the immediate cause of the war which followed, for the Germans were led to believe that Benedetti had insulted the king, and the French that the king had insulted the ambassador. Benedetti was severely attacked in his own country for his conduct as ambassador, and the duc de Gramont attempted to throw upon him the blame for the failures of French diplomacy.
He answered the charges brought against him in a book, Ma Mission en Prusse (Paris, 1871), which still remains one of the most valuable authorities for the study of Bismarck's diplomacy. In this Benedetti successfully defends himself, and shows that he had kept his government well informed; he had even warned them a year before as to the proposed Hohenzollern candidature. Even if he had been outwitted by Bismarck in the matter of the treaty of 1866, the policy of the treaty was not his, but was that of E. Drouyn de Lluys. The idea of the annexation of part of Belgium to France had been suggested to him first by Bismarck; and the use to which Bismarck put the draft was not one which he could be expected to anticipate, for he had carried on the negotiations in good faith.
After the fall of the Empire he retired to Corsica. He lived to see his defence confirmed by later publications, which threw more light on the secret history of the times. He published in 1895 a volume of Essais diplomatiques, containing a full account of his mission to Ems, written in 1873; and in 1897 a second series dealing with the Eastern question. He died on the 28th of March 1900, while on a visit to Paris. He received the title of count from Napoleon.
See Rothan, La Politique Française en 1866 (Paris, 1879); and L'Affaire de Luxemburg (Paris, 1881); Sorel, Histoire diplomatique (Paris, 1875); Sybel, Die Begrundung des deutschen Reiches (Munich, 1889).