In 1798 he purchased Airthrey Castle from the Haldane family and was thereafter entitled Abercromby of Aithrey.[4]
He was promoted lieutenant-general in 1797, elected M.P. for the county of Clackmannan in the place of his brother Ralph in 1798, and was made governor of Edinburgh Castle in 1801—a post he held until his death—and a general in 1802. His increasing blindness - arising from an eye disease contracted before his return from India in 1797 - made it impossible for him ever again to take active service, and obliged him to resign his seat in parliament in 1802.[5]