At the coup d’etat of the 18th Fructidor (September 4) 1797, he was arrested and transported to French Guiana. Transferred to Oléron In 1799, he owed his liberty to Napoleon, after the 18th Brumaire. In 1801 he became councillor of state and director of the public treasury, and in 1802 a senator. In 1803 he negotiated the treaty by which Louisiana was ceded to the United States, and was rewarded by the First Consul with a gift of 152,000 francs. In 1805 he was made grand officer of the Legion of Honour and a count.
In return for these favours, he addressed Napoleon with servile compliments; yet in 1814 he helped to draw up the act of abdication of the emperor, and declared to the cour des comptes, with reference to the invasion of France by the allies, "united for the most beautiful of causes, it is long since we have been so free as we now are in the presence of the foreigner in arms." In June 1814, Louis XVIII named him peer of France and confirmed him in his office as president of the cour des comptes. Deprived of his positions by Napoleon during the Hundred Days he was appointed minister of justice in the ministry of the duc de Richelieu (August 1815). In this office he tried unsuccessfully to gain the confidence of the ultra-royalists,, and withdrew at the end of nine months (May 10, 1816).
In 1830, when Louis Philippe assumed the reins of government, Barbé-Marbois went, as president of the cour des comptes, to compliment him and was confirmed in his position. It was the sixth government he had served and all with servility. He held his office until April 1834, and died on the 12th of February 1837.