Early in March 1792 he was elected lieutenant-colonel of one of the battalions of the Eure-et-Loire; he took part in the defence of Verdun in 1792, and it fell to his lot to bear the proposals of capitulation to the Prussian camp. The spiritless conduct of the defenders excited the wrath of the revolutionary authorities, and Marceau was fortunate in escaping arrest and in finding re-employment as a captain in the regular service.
Early in 1793 he became with other officers "suspect", and spent some time in prison. On his release he hurried to take part in the defence of Saumur against the Vendéean Royalists, and distinguished himself at the combat of Saumur (10 June 1793) by gallantly rescuing the representative Bourbotte from the hands of the insurgents. The National Convention voted him the thanks of the country, and thenceforward he received rapid promotion. His conduct at Chantonnay (5 September 1793) won him the provisional rank of general of brigade. On 17 October 1793 he bore a great part in the victory of Cholet, and on the field of this battle began his friendship with Kléber. For the victory of Cholet Kléber was made general of division and Marceau confirmed as general of brigade. Their advice was of the greatest value to the generals in command, and the military talents of each were the complement of the other's.
Marceau, who became general of division (10 November 1793), succeeded to the chief command ad interim, and with his friend won important victories near Le Mans (12 - 13 December 1793) and Savenay (23 December 1793). After the battle of Le Mans, Marceau rescued and protected a young Royalist lady, Angélique des Mesliers. It is often supposed that he was in love with his prisoner; but even the help of the commander-in-chief did not save her from the guillotine (22 January 1794). Marceau had already retired from the war, exhausted by the fatigues of the campaign, and he and Kléber were saved from arrest and execution only by the intervention of Bourbotte. Marceau became engaged about this time to Agathe Leprêtre de Châteaugiron, but his constant military employment, his broken health, and the opposition of the comte de Châteaugiron on the one hand and of Marceau’s devoted half-sister Emira, wife of the Republican politician Sergent, on the other, prevented the realisation of his hopes.
After spending the winter of 1793 - 1794 in Paris, Marceau took a command in the army under Jourdan, in which Kléber also served. He took part in the various battles about Charleroi, and at the final victory of Fleurus (26 June 1794) he had a horse shot under him. He distinguished himself again at Jülich and at Aldenhoven, and stormed the lines of Koblenz on 23 October 1794.
With the Army of the Sambre and Meuse he took his share in the campaign of 1795 on the Rhine and the Lahn, distinguishing himself particularly with Kléber in the fighting about Neuwied (18 - 19 October 1796), and at Sulzbach (17 December 1796). In the campaign of 1796 the famous invasion of Germany by the armies of Jourdan and Moreau ended in disaster, and Marceau's men covered Jourdan's retreat over the Rhine. He fought the desperate actions on the Lahn (16 and 18 September 1796), and at Altenkirchen on 19 September 1796 received a mortal wound, of which he died two days later, at the early age of twenty-seven.
The Austrians vied with Marceau's own countrymen in doing honour to the dead general. His body was burned, and his ashes, which at the time were placed under a pyramid designed by Kléber, were transferred in 1889 to the Pantheon at Paris.
See Maze, Le Général Marceau (1889); Parfait, Le Général Marceau (1892); and T. C. Johnson, Marceau (London, 1896).