In May of 1920, the Self Determination for Ireland League of Canada and Newfoundland (SDIL), an Irish republican organization, was founded in Montreal. The League opposed the actions of the British government of David Lloyd George at the time of the Anglo-Irish War (1919-1921), but it primarily presented itself as a Canadian organization. This article will describe the founding and evolution of this association still neglected by Irish-Canadian historiography. Deliberately focused on the experience of the SDIL in Quebec, the article highlights that two former Irish nationalist traditions clashed in the province: one, constitutional autonomist, and the other, republican. Despite this division of Irish-Quebec nationalist forces, the involvement of French-Canadian elites in the SDIL contributed to making the League a success in Quebec. At the time, journalists and politicians like Omer Héroux, Armand Lavergne and Henri Bourassa effectively supported the goals of the SDIL. This pragmatic agreement between Irish and French-Canadian coreligionsists who had often clashed at the beginning of the twentieth century (especially on the subject of French education in Canadian schools) incidentally constituted one of the original elements of the business of the SDIL. [ABSTRACT FROM AUTHOR]