Langbehn was born in Hadersleben in what was then the Duchy of Schleswig, on 26 March 1851, the third of four sons. His father, a philologist, was dismissed from his position as the assistant principal at the local "gymnasium" shortly after Julius's birth, a result of a campaign to suppress German nationalism in southern Denmark following the First Schleswig War and the Revolutions of 1848. The Langbehn family eventually settled in Kiel, where Julius entered the "gymnasium" in 1863. After graduation, he entered the University of Kiel for a degree in the natural sciences. At the age of 19, he enlisted in the Prussian Army following the outbreak of the Franco-Prussian War in 1870. He fought in the battles of Orleans and Le Mans in December 1870 and January 1871, respectively. Langbehn's military service left him with a profound distaste for war.