He was the son of Victor, Prince Napoléon and his wife Princess Clémentine of Belgium, daughter of King Leopold II of the Belgians and Archduchess Marie Henriette of Austria.

Leopold II's mother, Princess Louise-Marie of Orléans, was the eldest daughter of King Louis Philippe I, ruler of France during the July Monarchy.

When his father died on 3 May 1926, the 12-year-old Prince Louis succeeded as the Bonapartist pretender to the Imperial throne of France, his mother acting as regent until he came of age.

His offer was refused, and so he assumed the nom de guerre of "Louis Blanchard" and joined the French Foreign Legion, seeing action in North Africa before being demobilised in 1941, following the Second Armistice at Compiègne.

Prince Louis himself narrowly escaped death a month later when, on 28 August, he was badly wounded as part of a seven-man patrol that came under attack; he was the sole survivor.