Clarke was born in Landrecies, northern France, on 18 October 1765,[1] to Irish parents from Lisdowney, County Kilkenny.

In September 1781, Clarke entered the Military School of Paris as a cadet, joining the army in November 1782 as a second lieutenant in Berwick's Regiment.

[1] With the outbreak of the French Revolutionary Wars in 1792, Clarke was posted to the Army of the Rhine, distinguishing himself at the capture of Speyer in September 1792, and was responsible for covering the retreat to Worms in March 1793.

[1] Appointed Chief of Staff of that army the next month, in October he fell under suspicion and was suspended, arrested and briefly imprisoned.

[1] After his release, Clarke lived in Alsace until Lazare Carnot found him a post at the Directory's Topographical Bureau and restored him to his rank.

[1] After being admitted to the army reserve, Clarke supported the coup d'état of 18 Brumaire that brought Bonaparte to power.

After Napoleon's abdication, Clarke was replaced as Minister of War by Dupont de l'Étang but King Louis XVIII made him a Peer of France.

When Napoleon landed in Southern France in March 1815 to reclaim his throne (the "Hundred Days"), Clarke was again made Minister of War and served until the Bourbon government fled.