In 1804, Serrant joined the 5th Line Infantry Regiment, taking part in the campaign in
Venice before his regiment was sent to occupy
Dalmatia. He directed the capture of
Curzola and was then tasked with defending
Ragusa by General
Lauriston. There, he earned his rank of battalion commander on 21 June 1806, and the cross of knight of the
Legion of Honour. Serrant then took part in the Battle of Debilibriche, and was wounded and taken prisoner during the Battle of Gospich. He was exchanged and appointed colonel of the 3rd regiment of Croatian chasseurs ("Ogulin Regiment"). During the
battle of Ostrovno, on 25 and 26 July, he was wounded while protecting the cavalry of
Joachim Murat, and he was promoted to the rank of officer of the Legion of Honour five days later. Promoted to
brigadier general on 29 September 1812, he was wounded at the
Battle of Maloyaroslavets on 24 October, then led his regiment during the retreat before being taken prisoner at
Vilnius on 9 December. He escaped, crossed Poland alone and rejoined Beauharnais at
Magdeburg. Back in France, Serrant was placed on convalescent leave on 2 April 1813. Employed in the 7th military division on 10 January 1814, he served under
Joseph Marie Dessaix in Savoy. He captured
Annecy on 24 February, then the Gorges des Usses on 26 February, served in the Battle of
Saint-Julien on 1 March, and was victorious again in Annecy on 23 March 1814. He was placed on inactive status on 20 June 1814 and made a Knight of Saint Louis on 14 November. == Restoration ==