Prévost was enlisted as a conscript for a 6-year military service on April 11, 1855, replacing his older brother. Being of large stature and burly, he was incorporated into the 4th Cuirassiers regiment before moving on October 14, 1856 to the 2nd Cuirassier Regiment of the Imperial Guard and the 12th Cuirassier Regiment, with whom he participated in the Italian campaign, for which he received the commemorative medal. On December 31, 1861, he was released and given a certificate of good conduct.