Chief Master of Horses at the court of Gotha in 1764. Colonel of Cavalry, Commander of the Horse Guards and Director of the War Commission from 1751 to 1768.
Boswell visited the court of Saxe-Gotha in mid-October 1764 and on the 17th noted that he "found the stile of this court easy and cordial. I am already well with [...] [t]he Grand Ecuier", by which he probably means von Benkendorf, then the Chief Master of Horse. On October 18 von Benkendorf lent Boswell "a genteel Domino, white with red Ribbands."
On October 20, when Boswell went to take leave of the Duke and the gentlemen of the court, Benkendorf told Boswell that he was welcome to come back to Gotha and stay longer another time.