Barrois was born on 30 October 1774 at Ligny-en-Barrois in what later became the Meuse department. His father was a baker. On 12 August 1793, Barrois enlisted in the Éclaireurs (Scouts) of the Meuse and became a lieutenant exactly one month later. He fought at the Battle of Wattignies on 12–13 October 1793. His unit belonged to the division of Pierre Raphaël Paillot de Beauregard. This division was described by one historian as, "bad troops under a bad general", and performed poorly in the action. In 1794, the Éclaireurs of the Meuse were amalgamated with the Chasseurs of Cévennes to become part of the 9th Light Infantry Regiment.