This article explores the extent to which the traditional Catholic philosophies of Thomas Aquinas influence the Irish political imagination in the nineteenth century. It looks first to Pope Leo XIII, one of the leading proponents of restoring Thomism into mainstream Catholic political thought, and the author of the influential encyclical Rerum Novarum (1891). The article examines how the Irish Land War during the 1880s influenced the development and audience of the encyclical. Finally, it analyzes how the Thomistic principles which served as the foundations of Rerum Novarum were used by the lower-class Irish Catholic laity to legitimize incidences of protest and resistance which were considered morally illicit by the Catholic Church. In doing so, the article demonstrates how Catholicism and Thomistic philosophy influenced the way in which Irish Catholics perceived their relationship with the state and their rights as citizens.