After the First World War, he served as an advisor to the Royal Yugoslav Army and was named an instructor at the French High Mountain Military School.

Béthouart commanded the French 1st Division of Chasseurs (elite light infantry) in the Norwegian campaign in 1940, serving in the area of Narvik.

In August 1944, Béthouart briefly served as the Chief of Staff of Armée B, later known as the French First Army.

He fought with 140,000 men in Alsace but became famous for his part in the offensive in Germany with his corps becoming the first Allied troops to reach the Danube and enter Austria.

His corps is credited with taking 101,556 Germans prisoner during the campaigns to liberate France and invade Germany.