On 6 May 1904, he presented his credentials as Ambassador of the Dual Monarchy at the Court of St. James's, a promotion over the heads of many of his seniors that had come at the request of his second cousin King Edward VII.
The diplomat Count Albert von Mensdorff-Pouilly-Dietrichstein was a younger son of Prince Alexander Constantin.
At the outbreak of the Bohemian Revolt and the Thirty Years' War, in 1618, Dietrichstein fled to Vienna but returned after Emperor Ferdinand II's decisive victory at the Battle of White Mountain and was appointed Governor of Mähren from 1621 to 1628.