Vansittart was born in Bloomsbury in Middlesex, the third son of Arthur van Sittart (1691–1760), and his wife Martha, daughter of Sir John Stonhouse, 3rd Baronet.

Educated at Reading School and at Winchester College, Henry Vansittart joined the society of the Franciscans, or the Hellfire Club, at Medmenham.

Practically all the company's servants were traders in their private capacity, and as they claimed various privileges and exemptions this system was detrimental to the interests of the native princes and gave rise to an enormous amount of corruption.

Reprisals on the part of the subadar were followed by war and, annoyed at the failure of his pacific schemes, Vansittart resigned on 28 November 1764 and returned to England.

The mission left England in September 1769, visited Cape Town where they were last reported, embarking, on 27 December 1769, but the ship in which they sailed, the frigate Aurora, was lost at sea,[2] apparently foundered with all hands.