10th son of Hans Christoph, liberal Dutch and German diplomat and politician, who played a prominent part in the German Revolution of 1848, attempting to institute the Kleindeutsch (“small German”) solution to German unification, which aimed at excluding Austria's non-German territories.

Gagern, like his two prominent brothers, a nationalist and member of the Pan-German student Burschenschaft, was elected to the 1848 Frankfurt national assembly, where he served as vice president of the constitutional committee and undersecretary of state in the German Reich ministry of foreign affairs. In the spring of 1849 he led the unsuccessful “Gagern” mission, which tried to persuade the German princes to offer the imperial crown to the Prussian king Frederick William IV. Disillusioned with Prussia and the failure of the Kleindeutsch solution to German unification, Gagern entered the Austrian foreign service in 1855 but never again held a significant post.