Leclerc remained in the French Army and on the outbreak of the Second World War was a captain in the 4th Division. When the German Army began its Western Offensive Leclerc and his troops moved into Belgium. Serving under General Alphonse Juin, his troops were attacked by General Walther von Reichenau and the 6th Army. Forced to retreat they were pushed back into France.
On 15th June 1940, Leclerc received a serious head wound while fighting at the Aube River and had to be evacuated to a hospital at Tonnerre. He left just before the Germans arrived and managed to escape to Spain. Eventually he joined General Charles De Gaulle in London on 25th July.
After being promoted to the rank of major, he was sent with Free French troops to the Cameroons in August 1940. This small group of men soon overcame all Vichy resistance and the territory was taken from the control of Henri-Philippe Petain.
On 22nd November 1940, De Gaulle appointed Leclerc as military commandant of Chad. Leclerc led his troops on several raids on the Italian Army stationed in neighbouring Libya. This included the capture of Koufa in March 1941.
In November 1941, Charles De Gaulle ordered Leclerc to link up with General Bernard Montgomery and the 8th Army fighting General Erwin Rommel and the Deutsches Afrika Korps. Leclerc's campaign was a great success and he entered Tripoli on 25th January 1943. Now serving under Montgomery, his renamed 2nd French Light Infantry Division took part in the advance on Tunis. On 5th May 1941 Leclerc was appointed commander of the 2nd Armed Division in Morocco.
Leclerc served under General George Patton during the invasion of Normandy. Leclerc fought his way into Paris on 25th August 1944 and later that day accepted the German surrender of the city. He also took part in the advance into Nazi Germany.
After the death of Adolf Hitler and the German surrender, Leclerc was appointed commander-in-chief of French troops fighting the Japanese Army in the Far East. However, soon after arriving in Indochina Japan also surrendered.
Leclerc remained in Saigon until being appointed inspector of land troops in North Africa in February 1947. Jacques Leclerc was killed on 28th November 1947 when his plane crashed while landing at Colomb-Bechar.