His Writings
 By 1825, Carleton, who had left the Roman Catholic Church for the (Anglican) Church of Ireland, and took the opportunity given him by an evangelical clergyman of that church, Caesar Otway, to use his journalistic talents for such proselytising purposes as satirising Catholic pilgrimages to 'St Patrick's Purgatory' at Lough Derg. Further writings in the Christian Examiner & Church of Ireland Magazine led, in 1829 and 1833, to the publication of what is probably Carleton's best known work: Traits and Stories of the Irish Peasantry - a tableau of the life of the country people of the north of Ireland before the famines of the 1840s altered their pattern of existence forever. There then followed such novels as Fardorougha the Miser (1839), Valentine McClutchy (1845), The Black Prophet (1847), The Emigrants of Ahadarra (1848), The Tithe Proctor (1849), The Squanders of Castle Squander (1852) in which he addresses many of the issues affecting the Ireland of his day such as the influence of the Established Church and landlordism, poverty, famine and emigration.

His Language
 Because of Carleton’s attempts to appeal to an English readership, contrasting voices are found in his work: the voice of the earnest novelist, influenced by such writers as Thackeray and the English literary tradition and adopted to address a sophisticated audience, frequently gives way to a colourful Hiberno-English dialect through which his Irish country people converse about their loves, problems and preoccupations. This ability to present a way of life unknown to his readers remained with Carleton even though he became increasingly detached from his roots. He re-visited the Clogher Valley only once after his departure in 1817.

The Summer School
 His last project, uncompleted when he died in 1869, was his autobiography. D.J. O’Donoghue wrote a biographical sequel to this in 1896. The Autobiography was re-issued through the efforts of the Summer School Committee in 1996.