Couple of things - As Suffet points out, Wofe Tone was a Protestant, as were many of the leaders of the United Irishmen. By the time the rising came about however, the UI were in such disarray, mostly as the result of political splits over the AIMS of the group - more radical elements wanted a republic that would exclude some portion of the current residents of Ireland - others wanted a "Catholic" republic, much to the chagrin of the members of the Church of Ireland who were in positions of authority of the UI. It was this organizational disarray which led to the uncoordinated efforts in the eventual rising, which were further polarized by actions of radical elements in South Eastern Ireland. In short, it was a major CF.
The words are generally attributed to John Casey. The tune is traditional, with variants found in Ireland and Scotland. Which version came first? I don't think anyone can tell.