Creighton was heavily influenced by Harold Innis and took an economic approach to Canadian History. His main contribution was the development of the Laurentian Thesis, which described the basis of Canadian history by looking at the geography and the nation's dependence on the major centres. His two most important works are The Commercial Empire of the St. Lawrence (1937) and his two volume biography of John A. Macdonald.
In later years Creighton turned to expressing himself in the media. An intensive Canadian nationalist his opinions have often been criticized, especially his anti-Quebec views. He died in Collingwood, Ontario in 1979.
Creighton was regarded by many as the foremost historian of his day and his influence is still strongly felt today. Many of Canada's top historians studied under Creighton, such as Micheal Bliss, and Creighton's view of Canadian history is still often studied.