Northern peatlands are significant contributors to global biogeochemical cycles. In Canada alone, peatlands cover over a tenth of the land surface and store over half of the country’s terrestrial carbon. Their ability to function as a carbon sink is inextricably linked to hydrological conditions defined by an intricate web of feedbacks from numerous autogenic (internal) and allogenic (external) drivers. Research over the last forty years has been focused on understanding the importance of each driver, as such knowledge is necessary to foresee how these landscapes might respond climate change. However, one external driver - the activity of beaver (Castor canadensis in North America and C. fiber in Eurasia) - has received little attention, even though beaver have inhabited northern peatlands for many thousands of years. Identified as a keystone species and ecosystem engineer, beaver can alter the physical, hydrological, and biogeochemical function of landscapes on a scale comparable to that of humans. Thus, the primary goal of this dissertation was to enhance our understanding of how beaver activity alters peatland function and transforms these landscapes over time. To achieve this goal, the associated impacts of beaver activity were studied over numerous scales, mostly in the montane peatlands of Alberta, Canada, via the collection and analyses of field data comprised of different physiographic, hydrological and soil variables.