This thesis explores how a variety of political, religious and social determinants counterbalanced each other to legitimise a new canon, or canons, in post-Treaty Ireland. 'Participants' to be discussed in the making of the Irish canon included members of the Educational Board, university faculties, clerics, textbook editors and anthologists, historians, creative writers, literary critics, politicians, censors, and so on. The different traditions and perspectives they represent complicate the formulation of the canon through which many antagonistic ideologies give shape to the various versions of Irishness. The thesis also examines how and why some writers did not attract critical attention in mid-twentieth century Ireland, and what kinds of writing were deemed most 'canonical', when political and religious ideologies were more influential than other factors. To demonstrate how the formation of the Irish nation had impacts on the making of an Irish canon, this thesis will discuss relevant issues at institutional and textual levels. The institutional, as the first three chapters will elaborate, will focus on Irish education from primary to tertiary levels. These three chapters will reveal how the teaching of Irish literature might have significantly de-Anglicised Irish pupils, and how it sought to secure an Irish national identity. The latter four chapters, following the demonstration of the success and failure, of educational de-Anglicisation, will draw attention to literary works per se, to see why certain choices of themes would be admitted to, or left out of, the canon, and under what circumstances. Although both anthologists and many creative writers were interested in the topics of Irish history, the latter seemed to be more capable of introducing historical subjects from non-nationalistic or sometimes comic or feminist perspectives -- which caused some of their works to be dismissed from the nationalistic canon. The writers to be discussed in this thesis include Daniel Corkery, J. Q Farrell, Denis Johnston, Mary Lavin, Iris Murdoch, Kate O'Brien, Frank O'Connor, Liam O'Flaherty, and James Plunkett.