This thesis provides a history of the relationship between Prime Minister William Lyon Mackenzie King and the Prairie region of Canada. It offers insight into the career of Canada's longest serving prime minister and his handling of one of the most politically complex regions in the nation. Mackenzie King entered the leadership of the national Liberal Party in 1919 with a remarkably sympathetic attitude toward the Prairie West. This attitude translated into federal policies directed at regaining Liberal support in the region during King's early administrations. By the time of his retirement in 1948, his attitude had undergone dramatic transition and the region responded in kind. The roots of the decline in Prairie Liberalism are buried within the Mackenzie King era and a study of this phenomenon helps explain the place of the West in Canada.