Knocknagow was published in 1879, and rapidly became the most popular of all Irish novels. Its influence derives mainly from its political importance rather than its literary quality, which is about average for a best-seller but not outstanding. In this it resembles The Women's Room and The Ragged-Trousered Philanthropists, two other polemical novels which were very important politically but marginal as works of literary art. It attacks the evils of the landlord system in Ireland, and indirectly the English rule which supported that system. Kickham himself was a leading nationalist, and was imprisoned for his opinions.
For many years Knocknagow was the book - along with a prayerbook and Old Moore's Almanac most likely to be found in any Irish home. Most Irish writers born between 1870 and 1950 would have read it as children. Yeats described it as "The most honest of Irish novels" and Con Houlihan as "The greatest Irish novel." For all its sentimentality and inept plotting, it gives a very accurate picture of rural Irish life in the nineteenth century. Furthermore, it is one of the few such novels which was written by one of the ordinary people. Almost all the other writers who dealt with the rural poor were either of the landlord class themselves Lady Gregory, J.M. Synge, Somerville and Ross, Emily Lawless, Maria Edgeworth or urban Protestant middle-class George A. Birmingham, Charles Lever, Dion Boucicault, Samuel Lover. However sympathetic and well-writen their accounts, they were written from the outside looking in. Knockangow was written from the inside.