[3] He then sat as a Knight of the Shire for Suffolk until 1805,[4] when he succeeded his father in the marquessate and entered the House of Lords.
[1] In 1807 he was appointed Master of the Buckhounds, a post he held until his death fourteen years later.
[5] On 26 May 1803 he was appointed Colonel of the East Suffolk Militia, and continued in command until his death.
They had five daughters, including Lady Jane Cornwallis, wife of Richard Griffin, 3rd Baron Braybrooke, and Lady Jemima Cornwallis, wife of Edward Eliot, 3rd Earl of St Germans.
The marquessate became extinct on his death while he was succeeded in his remaining titles by his uncle, the Right Reverend James Cornwallis.