[1][3] After succeeding to the estates of his maternal uncle in 1814, he assumed by Royal licence the surname of Mann in lieu of Cornwallis.
[4] He became known by the courtesy title Viscount Brome in 1823 after his father succeeded in the earldom of Cornwallis.
After his first wife's death, he married secondly Laura, daughter of William Hayes, in 1829.
After his second wife's death, he married thirdly Julia, daughter of Thomas Bacon of Redlands House at Reading in Berkshire, in 1842.
Cornwallis's daughter from his first marriage, Lady Jemima Isabella, married Charles Wykeham Martin.