On the death of Thomas Secker in 1768, his friendship with the then-prime minister, the Duke of Grafton, resulted in his appointment as Archbishop of Canterbury. As archbishop, his sociability and geniality made him popular. He was a consistent supporter of the administration of Lord North, and led efforts in support of dispossessed Anglican clergy in the American colonies during the American Revolution.
On the whole, Cornwallis has generally been judged as a competent administrator, but an uninspiring leader of the eighteenth century church - a typical product of eighteenth century latitudinarianism, whose lack of zeal paved the way for the differing responses of both the Evangelicals and the Oxford Movement in the early 19th century.
