Guyot took part to the Wars of the Third and Fourth Coalition with the Grande Armée, holding the rank of squadron commander in the Guard "chasseurs-à-cheval" regiment and being noted for bravery at the Austerlitz and Eylau. He fought at the minor Battle of Waren-Nossentin on 1 November 1806. A colonel in the Imperial Guard in 1807, he was created a baron of the Empire the next year and given a position in Lefebvre-Desnouettes's Guard light cavalry, commanding the Emperor's escort during the latter's brief campaign in Spain. In 1809, after the bloody battle of Aspern-Essling, Guyot was given the function of colonel commander of the Guard "chasseurs-à-cheval" and six weeks later he led a famous charge at the battle of Wagram. This action would bring him the rank of brigadier general. A Chamberlain of Emperor Napoleon I from March 1810, he was subsequently sent to Spain, where he won a promotion to general of division in 1811. During the Russian campaign and subsequent War of the Sixth Coalition, Guyot would serve as commander of the Guard "chasseurs-à-cheval". In the 1813 campaign in Saxony, he was wounded at the battle of Lützen and led a brilliant charge at the battle of Bautzen, before being made prisoner at the battle of Kulm, in August. Released after an exchange of prisoners, Guyot took part to the epic battle of Leipzig, before being created a count of the Empire in November of that year. The 1814 campaign in France saw general Guyot at the heart of the action, commanding cavalry at La Rothière, Champaubert and Craonne.