Heinrich Bewerunge is acknowledged internationally as a musician and scholar of exceptional ability, but to date there has been limited detailed engagement with his work and influence. This thesis reassesses his status in Ireland and abroad, through an examination and analysis of primary sources including large correspondence archives, administrative documents, music manuscripts, and extensive surveys of media reportage. It fills substantial lacunae in his biography, including his social and educational background, the practicalities of his work in St Patrick’s College Maynooth, and the much wider scope of his crucial role and influence as an educator and facilitator. The study argues that Bewerunge’s identification with the Cecilian movement for church music reform has been over-emphasized, to the detriment of his expertise and contributions as a musicologist, scholar, and educator. It establishes his pioneering involvement in Irish traditional music as a preservationist and ethnomusicologist; and repositions his role in the development of secular music education in Ireland. To date, his reputation as a scholar has largely rested on his seminal critiques of the Vatican editions of plainchant. This research has discovered a significant number of previously overlooked published articles; an appraisal of these, along with his known work, vindicates his standing in a broader field of scholarship. The thesis also proves that an influential English plainchant treatise was partly authored by him. Bewerunge’s compositional output has been reassessed, in light of newly-discovered works and a previously unexamined aspect of his legacy: that of plainchant harmonisation. Finally, this study highlights the ruinous impact of the First World War on Bewerunge’s career, by analysing the deeply prejudiced attacks on his reputation (ostensibly motivated by anti-German nationalism) which have affected his reception ever since.