Vandamme enlisted in the army in 1786 and rapidly rose through the ranks. At the outbreak of the French Revolutionary Wars in 1793 he was a Brigadier General. He served in this rank in the campaigns of 1794 in the Low Countries, 1795 on the Rhine and 1796 in Germany. He was court-martialled for looting and suspended. Reinstated, he fought at the First Battle of Stockach on 25 March 1799, but disagreement with General Jean Moreau led to his being sent to occupation duties in Holland. At the Battle of Austerlitz in 1805 he led his division, alongside Gen. St. Hilaire's, as part of Marshal Soult's IV Corps in the charge that captured the Pratzen Heights. For his leadership he was awarded the Grand Eagle of the Legion of Honour.