Upon the outbreak of the French Revolution, Compans enlisted as a volunteer in 1789.[citation needed] At age 23 he was promoted to captain in the 3rd battalion of the volunteers of the Haute-Garonne.[1] In 1793 his commanding general Dugommier promoted him to command a battalion in the brigade of Jean Lannes. Compans distinguished himself in the campaigns in Spain and Italy (1793-1797). In 1798 he was put in command of a corps of 16.000 men with which he took the towns of Fossano and Savigliano.[citation needed] In June 1799 he received a temporary promotion to General de brigade, which was made permanent in October.[1] In 1800 Compans was wounded by a musket ball at San Giacomo. Having recovered, he distinguished himself at Montebello and Marengo.
After Napoleon's abdication, Compans served Louis XVIII of France on the War Council. During the Hundred Days he rejoined Napoleon but declined a command in the Army of the North. Having been named a Pair of France by Louis XVIII, in the trial of Marshal Ney he voted for the death penalty. His name is inscribed on the eastern column of the Arc de Triomphe.[1]