[1] De Witte entered the Royal Military Academy in 1874.

In 1880, he requested a transfer to the cavalry and was posted to the 2nd Chasseurs à Cheval.

He received his Brevet d'état-major (BEM) in 1887, and between 1906 and 1910 served as commander of the 1st Guides Regiment.

He was promoted to lieutenant-general in August 1914, just 6 days before commanding his division at the Battle of Haelen.

The Belgian victory at the battle, nicknamed the "Battle of the Silver Helmets" after the cavalry helmets left on the battlefield after the fighting, was an important incident of the campaign.