After being dismissed from the army for a year and a half for having noble blood, he resumed his military career and was wounded at Biberach and Kehl.

At the start of the Napoleonic Wars, Marcognet was a general officer commanding a brigade in Marshal of France Michel Ney's corps.

Marcognet commanded a division in the Italian campaign of 1813-1814, fighting at Caldiero, Boara Pisani, the Mincio, and other actions.

With his new unit he fought under Jean Victor Marie Moreau at the Battle of Ettlingen on 9 July 1796 and was promoted to chef de bataillon (major) the following day.

[7] As the head of Johann Kollowrat's Left Center Column advanced along the main highway from the east, they bumped into Marcognet's 108th Line at about 7:00 AM.

[8] Franz Löpper, who led the Austro-Bavarian advance guard, immediately ordered his 5,341 foot soldiers and 1,319 cavalrymen to attack.

Using a forest trail, Lelio Spannochi secretly posted the Sebottendorf Grenadier Battalion on the flank of the 108th Line and charged.

[1] In the War of the Third Coalition he was assigned to Jean-Pierre Firmin Malher's 3rd Division of Marshal Michel Ney's VI Corps.

His troops overran the Austrian covering force, capturing Konstantin Ghilian Karl d'Aspré, 200 men, and two cannons.

[12] At the start of the War of the Fourth Coalition, Marcognet commanded a brigade in Gaspard Amédée Gardanne's division of Marshal Michel Ney's VI Corps.

After initial success, a massed Russian cavalry charge against Bisson's left flank stopped Ney's attack cold.

However, Claude Perrin Victor's corps drove back their enemies, allowing Ney's troops to rally and capture the town of Pravdinsk (Friedland).

When a Spanish army under Don Lorenzo Duke of Del Parque took a position at Tamames, Marchand rushed to engage it with 14,000 soldiers and 14 guns.

When the Spanish counterattacked, Marcognet's troops fled back down the ridge, prompting Marchand to bring up his reserves and call off the battle.

[28] After rejoining his division, his brigade fought in rear guard actions at Redinha, Casal Novo, and Foz do Arouce between 12 and 15 March.

By recalling the Italian units serving under Marshal Louis Gabriel Suchet in Spain and mass conscription, an entirely new army was formed and placed under Napoleon's step-son, Eugène de Beauharnais.

[32] After the Austrian Empire's declaration of war on 12 August 1813, Eugène moved his army east to defend Illyria.

[34] In early November, Eugène reorganized the army[35] and Marcognet emerged as commander of the 4th Division in Paul Grenier's corps.

[39] Having given his enemies a sharp blow, Eugène fell back to Verona, leaving Marcognet's division on the east bank of the Adige at San Michele.

[41] After De Conchy's brigade was defeated on the Lower Adige, Eugène sent Marcognet's entire division to defend the area in early December.

[42] With his own division plus Nicolas Schmitz's brigade of Rouyer's, Marcognet attacked Anton Gundacker von Starhemberg's 6,000 Austrians at Boara Pisani on 8 December 1813.

The divisions of Rouyer and Quesnel led the attack with cavalry on both flanks, supported by Marcognet and Teodoro Lechi's Italian Guard.

[45] On the night of 9 February 1814, Bellegarde pushed 10,000 foot soldiers and 2,000 horsemen across the river at Borghetto near Valeggio sul Mincio.

After this action, Bellegarde abandoned any attempt to force the Mincio and waited for Joachim Murat's Neapolitan army to join him from southern Italy.

[55] After d'Erlon's attack commenced, Joachim Jerome Quiot du Passage's 1st Division encountered the British 95th Rifles in the gravel pit and inclined to its right.

The Netherlands 7th and 8th National Militia Battalions engaged in a fire fight with the French skirmishers, taking some loss.

The French fired a tremendous volley from 400 muskets which inflicted heavy losses on the militiamen, who immediately retired on the second line.

The British cavalrymen, mounted on large horses, rained sword-cuts on the French foot soldiers as they hewed a bloody path through the formation.

[60] Late in the day, Marcognet got together a rump of his division in order to support the final assault on La Haye Sainte.

[1] He died in Paris on 19 December 1854 and is buried in the Père Lachaise Cemetery with his wife, Julie Catherine Le Monnier (1795–1866).