Sir Richard Musgrave (1746-1818) is properly best known as the author of Memoirs of the various rebellions in Ireland - the seminal history of the 1798 Rebellion published in 1801. A monumental, if ineffably partisan, work, it elicited a sharply divided response on its publication because of Musgrave’s portrayal of the Rebellion as an attempt by the Catholic population, instigated and guided by their clergy, to effect the extirpation of Protestants in their midst. This interpretation of the Rebellion has been shown to be profoundly misleading, yet Musgrave’s egregious chronicle has proved more influential than its rivals as a source of information on the origins and course of the Rebellion, and more ideologically influential because it was one of the key texts of early-nineteenth-century ultra-protestantism. This study of Musgrave seeks first to locate Memoirs of the various rebellions in Ireland in its eighteenth-century context, and, secondly, to establish the vital contribution it made to the opposition of ultra-protestants to the efforts of Catholics and liberal Protestants to promote Catholic emancipation. The picture that emerges from this work is of a voice of hitherto unappreciated significance in the pantheon of British and Irish ultraprotestantism, whose ideological and political impact was such as to necessitate a fundamental re-assessment of the politics of early nineteenth century Britain and Ireland.