 He was a prolific writer and wrote on a range of subjects.Cust was born to Reverend Henry Cockayne Cust, Canon of Windsor, who was the second son of Sir Brownlow Cust, 1st Baron Brownlow (1744–1807), and Lady Anna Maria Elizabeth Needham, daughter of the Earl of Kilmorey.His elder brothers were Henry Cockayne-Cust and Sir Reginald Cust.