Reynier joined the French Army as a gunner in 1792 and was drafted in October into the Army of the North, in which he saw action at the Battle of Jemappes that year and at Neerwinden in 1793. He was promoted to brigade general in January 1795, and received the assignment of chief of staff of the Army of the Rhine and Moselle under Moreau in March 1796, soon becoming general of division in November of the same year.