After re-entering the French service in 1814 he led a cavalry division at Gué-à-Tresmes, Laon, Reims, Fère-Champenoise and Paris.

He transferred again to the Army of the Midi as an adjutant on 21 September 1792 and was involved in some campaigning before emerging as captain in the Legion of the Moselle on 8 December 1792.

[3] Merlin was wounded in the right arm by a saber stroke[1] at Steinbach on 15 October 1795 in a minor French victory during the retreat.

[11] The regiment participated in the Second Battle of Zurich on 25–26 September 1799 in Édouard Mortier's 8th Division of André Masséna's Army of the Danube.

[12] At the start of the 1800 campaign the 4th Hussars were assigned to Antoine Guillaume Delmas' division of Jean Victor Marie Moreau's Army of the Rhine.

[18] During the battle, the British commander Sir Arthur Wellesley ordered William Anson's cavalry brigade to charge the French.

About 150 yards (137 m) in front of the French defenders, the 1st Hussars of the King's German Legion and the 23rd Light Dragoons unwittingly charged into a hidden stream bed which toppled many horses and tumbled many riders to the ground.

Hastily reforming, the Germans and the left wing of the 23rd LD charged the French infantry drawn up in squares, were repulsed and withdrew.

Drake's and Allen's squadrons on the right wing of the 23rd LD rode past the squares and charged Merlin's cavalry brigade.

[20] King Joseph appointed Merlin to command his Royal Guard on 16 August, but he also led the light cavalry in the rout of the Spanish at the Battle of Ocaña on 18–19 November 1809 according to historian Charles Mullié.

[21] This is contradicted by Charles Oman who asserted that Antoine-Marie Paris d'Illins led the IV Corps cavalry at Ocaña.

On 2 March 1814 Friedrich von Kleist sent out a reconnaissance force of three cavalry regiments, five infantry battalions and two horse artillery batteries.

[28] During the Battle of Laon on 9 March, the corps of Marshal Auguste de Marmont and Bordesoulle were routed by a 7:30 pm Prussian surprise attack.

[29] At the Battle of Reims on 13 March, Merlin's division advanced on the extreme right flank with the task of stopping the Prussians from falling back toward the bridge at Sillery.

[30] On 14 March, Merlin's troopers were beaten in a skirmish with Friedrich von Katzeler's Prussian cavalry at Courcy, losing about 100 casualties.

[32] When the force led by Marshals Marmont and Mortier moved east, Merlin formed its advance guard.

On 23 March 1814 at Bergères, his troopers drove off an Allied foraging party, capturing 100 men and liberating 16 wagon loads of plunder.

[35] For the Battle of Paris on 30 March Merlin's division was reduced to 850 horsemen in the brigades of Pierre François Huber and Antoine Henri Latour-Foissac.

[36] Bordesoulle's corps and Louis Pierre Aimé Chastel's cavalry division were posted on the extreme right flank.

[37] After Napoleon abdicated, King Louis XVIII named Merlin inspector general of cavalry in the 5th Military Division and awarded him the Order of Saint-Louis on 19 July 1814.

[21] After the July Revolution, Merlin was first appointed cavalry inspector of the 38th arrondissement on 8 August 1830 and commander of Corsica on 9 September 1830.