On his return from a pedestrian tour in Italy, he addressed a memorial to the Due de Choiseul, urging him to embrace the cause of the Corsicans against the Genoese; and a public audience which he had with the minister on the subject led to a violent altercation, the result of which was a lettre de cachet which forced Dumouriez to leave France. But the expedition which he had advised being afterwards resolved on, Choiseul made him an honourable public reparation, and appointed him quartermaster-general of the troops. The political conjunctures of the times offered an unlimited scope for his fertility in diplomatic expedient, and he mingled in all the intrigues of the age. In 1770 he was sent on a secret mission to Poland with the view of neutralizing the efforts of Catherine II., and succeeded in seeming fifty senators for the cause of independence, effected a unity of action among the confederates, and disciplined a militia; but, when there was some appearance of the resurrection of Poland being effected, Choiseul lost his place, owing to the machinations of the Due d’Aiguillon and Madame Du Barry, and Dumouriez was recalled to Paris. He was soon, however, sent back on a similar mission by D’Aiguillon. He endeavoured to assist the revolutionists in Sweden, and to raise troops in the Hanse towns to menace Stockholm, but this was contrary to the views of the French cabinet; and the Due d’Aiguillon. having discovered his project, had him arrested and imprisoned in the Bastille for six months. He was afterwards sent to the castle of Caen, from which he was not released until the accession of Louis XVI.

Dumouriez had naturally little inclination to resume the connection with foreign politics which had proved so dangerous, and he accordingly devoted his attention to the iuternal economy of his own country. He wrote a memoir on the great importance that might be given to the harbour of Cherbourg, one result of which was that he was appointed governor of the place in 1778.

In 1788 Dumouriez w as promoted to the rank of majorgeneral. When the revolutionary movement began he pronounced in favour of political reform without breaking with the court. The connections which he held with the leading men of the Girondist party greatly advanced his political career. At the opening of the second legislative assembly he was appointed minister for foreign affairs in place of Delessart, but he held the position for only three months. During his short tenure of office he exerted himself to the utmost in reforming abuses, and in introducing the greatest economy into every department.

He held for one month the office of minister of war after the dismissal of his colleagues Roland, Servan, and Clavière. At length his own resignation followed, which increased his popularity. When the troops of the coalition advanced against France, he was appointed to the command of the army of the north as lieutenant-general under Marshal Luckner. He made a determined stand against the advance of die allies, which was decisively checked by the defeat inflicted on them at Valmy on the 20th September 1792. This was followed by a campaign in the Austrian Netherlands, in which Dumouriez was uniformly successful, until he was signally defeated by Coburg in the battle of Neerwinden in January 1793. The execution of Louis had estranged him from the republican party; and, when in consequence of his defeat he was recalled by the Convention and threatened with a charge of treason, he sought refuge in the camp of the Austrians, accompanied by the Due de Chartres (afterwards Louis Philippe) and his brother.

Lost without hope of return to his native country, Dumouriez wandered a long time an exile in Brussels, England, Switzerland, Germany, Denmark, and St Petersburg. At last in 1804 he took up his permanent residence in England, where the Government conferred on him a pension of £1200 a year. In 1814 and 1815 he endeavoured to procure from Louis XVIII. the baton of a marshal of France, but was refused. He died at Turville Park, near Henley-on-Thames, on the 14th March 1823. His memoirs, written by himself, were published at Hamburg in 1794. An enlarged edition, under the title La Vie et les Mémoires du General Dumouriez, appeared at Paris in 1822. Dumouriez was also the author of a large number of political pamphlets.