This thesis examines the 1946 Master Plan for the City and County of Saint John, a municipal plan produced between 1944 and its adoption in 1945 by the architect-planner John Campbell Merrett for the City of Saint John, New Brunswick. I examine this document as both a locally and nationally significant development in Canadian architectural and planning histories. Reviewing the many agencies, commissions, and individuals who influenced the development of the 1946 plan, this thesis proposes a broad interpretation of authorship. This thesis seeks two primary outcomes: first, to intervene in a local discourse that misrepresents the legacy of the plan to the detriment of the region’s architectural scholarship. Second, this thesis seeks to engage the 1946 plan in a national discourse that has yet to address the significant contribution of the city of Saint John to Canadian planning in the critical post-Second World War period of Canadian architectural production. This thesis argues that Merrett’s plan both anticipated and mitigated significant economic setbacks and greatly assisted the struggle of the city of Saint John in maintaining its status as a cultural and economic metropolis during the period. The 1946 plan raises foundational questions of Canadian federalism and its influence on the postwar built environment and highlights the continued national influence of Canada’s easternmost regions.