Hans Christoph von Gagern's eldest son, a German soldier and administrator, and military commander of several Dutch provinces, who served as chief of staff during the wars against the Belgian rebels opposing Dutch rule. Returning to Germany, he led the fight against the republican revolutionaries in Baden in 1848.

Interrupted in his studies at Göttingen by Napoleon's temporary return to power in 1815, Gagern fought and was wounded at Waterloo. Finishing his education at Heidelberg, he joined the Burschenschaft (German nationalist student movement), whose interests in German unification he was to share for the rest of his life. Gagern then entered the Dutch Army, eventually becoming chief of the general staff and serving under Prince Bernhard of Weimar in the unsuccessful attempt to suppress the Belgian revolt (1830–31). Twice he was military commander, first of North Holland (1842–44), then, after a journey to the Dutch East Indies and around the world, of South Holland, a post he held simultaneously with his governorship of The Hague. Returning to Germany at the outbreak of the 1848 revolution, he led the army against the rebels in Baden but was killed during the first encounter.