Son of Charles Cornwallis, 1st Earl Cornwallis (1700-1762) and Elizabeth Townshend (1698-1785). Brother of Charles Cornwallis (1738-1805), who was sometime Lord-Lieut. of Ireland and Commander in Chief in India. Married (1772) to Catherine Mann (1742-1811) in Lambeth Chapel.
Educated at Christ Church, Oxford. Bishop of Lichfield and Coventry (1781-1824). Dean of Canterbury (1781-1824), Dean in commendam of Windsor (1791-1794), Dean in commendam of Durham (1794-1824).1 He became the fourth Earl and 8th Baron Cornwallis in 1823, following the death of his nephew Charles Cornwallis, the third Earl.
According to Brown (1953), James Cornwallis was "[a]n aristocratic nonentity who owed his promotion to his uncle Archbishop [of Canterbury] Frederick Cornwallis".2
Boswell met Cornwallis in the company of Sir James Macdonald and others in Oxford on April 23, 1763.