[5] During the July 1203 siege of Constantinople, Louis was one of eight division commanders,[6] the others including Boniface of Montferrat (the crusade leader), Doge Enrico Dandolo (leader of the Venetians), Baldwin of Flanders (who controlled the largest division and later became Latin Emperor of Constantinople), and Baldwin's brother Henry.

Though she claimed to have forgotten his mother tongue to the crusaders, she held a private discussion with Louis without the help of any traductor.

Louis was later afflicted with a severe fever for months, and missed participating in the capture of Constantinople in 1204.

He had just recuperated when he participated in the Battle of Adrianople, where he was slain by a force of Cumans led by Kaloyan of Bulgaria ("Johanitza").

[8] Louis chased the enemy too far, exhausting his men and horses and stretching them over a broad plain, where he brought himself and the Emperor Baldwin I of Constantinople into a trap.