Konstantin von Benckendorff was born into Russia's distinctive Baltic nobility to a Baltic German family in Saint Petersburg, son of General Baron Christoph von Benckendorff [de] (Fredrikshamn, 12 January 1749 - Kolga, 10 June 1823), who served as the military governor of Livonia, and wife Baroness Anna Juliane Charlotte Schilling von Canstatt (Thalheim, 31 July 1744 - Riga, 11 March 1797), who held a high position at the Romanov Court as senior lady-in-waiting and best friend of Empress Maria Fyodorovna, and paternal grandson of Johann Michael von Benckendorff and wife Sophie von Löwenstern.
His other sister Maria von Benckendorff (14 February 1784 - 16 November 1841) married Ivan Georgievich Sevitsch.
Trained as a diplomat, he joined the army to take part in the concluding stages of the Napoleonic Wars, specifically in the taking of Kassel, Fulda, Hanau, Reims, and Soissons.
With the outbreak of the Russo-Persian War he returned to Russia, captured Echmiadzin and routed the Kurds near Erivan.
Benckendorff died of a fever that swept through the Russian army at the beginning of the Russo-Turkish War, 1828–1829.