1803–1806 Margaron received promotion to
general of brigade on 29 August 1803. He became a member of the
Légion d'Honneur on 11 December 1803 and became a commander of the Légion on 14 June 1804. He was first sent to join the cavalry camp at
Saint-Omer and later posted to
IV Corps under
Marshal Jean-de-Dieu Soult. He took part in the
War of the Third Coalition which ended with the
Battle of Austerlitz on 2 December 1805. At Austerlitz he commanded the IV Corps light cavalry brigade, which counted 12 squadrons from the 8th
Hussar and the 11th and 26th
Chasseurs à Cheval Regiments. During the 1805 campaign Margaron was wounded by bullets two times. After returning to France, he was placed on the inactive list on 11 April 1806, but was recalled to active duty on 28 July. At the
Battle of Jena on 14 October 1806, Margaron led one of Soult's two IV Corps light cavalry brigades. His brigade consisted of the 8th Hussars and 22nd Chasseurs à Cheval. At Jena, Soult attacked 5,000 Prussians under Friedrich Jacob von Holtzendorff guarding the northern flank. Surprised by French troops lunging at his left flank, Holtzendorff withdrew in good order, well covered by his cavalry. At length, Soult's light cavalry burst through the Prussian cavalry and light infantry screen and pounced on one of the retreating Prussian columns, capturing 400 men, six artillery pieces and two colors. After deploying his troops near the village of Nerkwitz, Holtzendorff found French infantry circling his left flank while Soult's cavalry charged from the front. The Prussian force collapsed; its cavalry rallied later, but the infantry fled from the field. Margaron's brigade fought at the
Battle of Lübeck on 6–7 November 1806.
Portugal In 1807 Margaron was assigned to the 1st Corps of Observation of the
Gironde under
Jean-Andoche Junot. Margaron and
Antoine Maurin led brigades in the 1,754-man cavalry division under
François Étienne de Kellermann. The mounted troops included one squadron each from the 1st, 3rd, 4th, 5th, 9th and 15th
Dragoon and 26th Chasseurs à Cheval Regiments. All squadrons counted between 236 and 262 troopers. With Spain's permission, Junot's force crossed the
Bidasoa River on 18 October 1807 and was in
Salamanca by 12 November, prepared to invade Portugal. Little did the Spanish know that Napoleon soon planned to overthrow their kingdom as well. Soon after Junot's corps launched the
1807 invasion of Portugal, logistical arrangements broke down and half the army's horses died. Nevertheless, on 30 November 1807, a 1,500-man French vanguard occupied
Lisbon, having faced no military opposition. Then cavalrymen then remounted themselves with confiscated horses. Soon afterward, Napoleon overthrew the
Kingdom of Spain in a political and military coup; this proved in the long run to be a gigantic blunder. French Imperial troops which were supposed to be reinforcements for Junot's corps seized several key Spanish fortresses during February 1808. Soon there were 118,000 French soldiers in the country. By trickery Napoleon deposed both
King Charles IV and his son
Prince Ferdinand and replaced them with his brother
Joseph Bonaparte. On 2 May 1808, the
Dos de Mayo Uprising began and by the end of the month the rebellion was spreading rapidly through Spain. By the beginning of June, Junot's line of communications with France through Spain was severed. The Portuguese revolt started in the north, but on 16 June the rebels in the south captured Maurin and the handful of French soldiers guarding
Faro. On 5 July, Junot sent Margaron with 3,000 troops on an expedition to
Tomar and
Leiria where he successfully stamped out the revolt. On 25 July, Junot ordered
Louis Henri Loison to lead an expedition east toward
Elvas. On 29 July, Loison's 8,800 soldiers and eight field guns encountered 2,900 Spanish and Portuguese regulars in the
Battle of Évora. Margaron personally led the 86th Line Infantry Regiment in smashing through the Allied center and capturing three cannons. The defeated Allied infantry retreated to
Évora which they and some poorly-armed townspeople tried to hold, but the French broke into the town and massacred 2,000 defenders. French casualties were 90 killed and 200 wounded, which they revenged by brutally sacking the town. Three days later, Loison received orders to return to Lisbon to repel a British invasion. On 2 August 1808
Sir Arthur Wellesley landed in Mondego Bay with 13,536 British troops. These were joined by 2,300 Portuguese soldiers. The expedition was soon reinforced by an additional 4,000 British troops. Wellesley beat 4,765 French troops under
Henri François Delaborde on 17 August in the
Battle of Roliça. This was followed by the
Battle of Vimeiro on 21 August where Wellesley lost 719 casualties out of a strength of 18,669 men. The defeated Junot suffered 1,800 casualties out of a total 16,622 men and lost 12 guns out of 23. Another source estimated Junot's total force at 10,300 infantry, 2,000 cavalry and 700 artillery. Margaron commanded the cavalry, which were all organized as provisional regiments. They were the 3rd, 4th and 5th Dragoons and the 1st Chasseurs à Cheval, plus 100 volunteers. At Vimeiro, Junot sent the 3rd Dragoons with one of his flanking brigades, leaving Margaron with three cavalry regiments. After his first three frontal attacks failed, Junot sent Kellermann with his grenadier reserve to strike at Vimeiro village. After a hand-to-hand struggle, the grenadiers were beaten and Margaron sent one regiment to cover their retreat. At this moment, 240 troopers of the British
20th Light Dragoons charged, broke through the French cavalry and began cutting down the grenadiers. Excited by their success, the British horsemen got out of control and pressed their charge too far. When Margaron unleashed his last two regiments, the light dragoons were lucky to get away with only 21 killed, including Colonel Taylor, 24 wounded and 11 captured.
1809–1814 In return for surrendering Portugal, the British repatriated Junot and his troops to France. When Junot's force was reassembled as the
VIII Corps, it was missing its cavalry because the provisional cavalry units were assigned to their proper regiments. Margaron was assigned to command the cavalry depots in
Deux-Sèvres and
Charente-Inférieure. He was appointed
Baron of the Empire on 29 January 1809. He went to Spain as part of the
II Corps in 1809 but returned to France on leave before the end of the year. Between 6 September 1810 and 22 July 1812, he commanded the department of
Haute-Loire. Margaron was transferred to the army in Germany and promoted to
general of division on 16 August 1813. During the
Battle of Leipzig on 16–19 October 1813 he commanded the 4,820-man garrison of
Leipzig, consisting of two brigades supported by two French horse artillery batteries of 12 total guns and a 4-gun half-battery. Annet Morio de L'isle led the French brigade which included the 2nd Battalions of the 96th and 103rd Line Infantry, the 4th Battalion of the 132nd Line and a converged battalion of the 35th/36th Light Infantry. Count Hochberg directed the
Grand Duchy of Baden brigade which was made up of one battalion of the 2nd Line Infantry and the Lingg Light Battalion. ==Later career==