One of his ancestors, another Baron Rosen, won distinction in command of the Astrakhanskii Cuirassier Regiment at the Battle of Borodino on September 7, 1812, for which he was noted in the official battlefield report to General Barclay de Tolly.

Rosen graduated from the University of Dorpat and the Imperial School of Jurisprudence,[2] and joined the Russian Foreign Ministry’s Asiatic Department, rising to head the Japan Bureau in 1875.

He helped draft the Treaty of Saint Petersburg (1875), in which Japan exchanged its claims over Sakhalin for undisputed sovereignty over the entire Kurile islands chain.

[2] However, after he was publicly critical over increasing Russian military activity on the Korean coast and the Yalu River, he was suddenly transferred to the rather symbolic post as Ambassador of Russia to the Kingdom of Bavaria in 1899.

"[4] After the Bolshevik takeover in November 1917 October Revolution and the subsequent persecution of the old political and social elites, Rosen and his family managed to escape from Russia with the help of Western diplomatic friends in the end of the year 1918.

[2][5] Rosen wrote a series of articles about European diplomacy and politics for The Saturday Evening Post covering the period from his first exile in Sweden to his life in the United States.