Initially chartered in 1883 to serve the needs of local millers in Minneapolis, the Soo would eventually come to join the Canadian Pacific line at Sault Ste. Marie, Ontario, with service to Montreal. In 1888, Canadian Pacific assumed controlling interest in the Soo Line, providing entry into the lucrative US market and levelling the playing field for the CPR to face the onslaught of ferocious competition from James J. Hill, the infamous American railway baron.

The "little railway that could" grew to attain giant-killer status, launching famous passenger trains from Minneapolis and St. Paul, meeting head-on the western expansion of the Great Northern Railway and viable, competitive routes to the Atlantic seaboard. Over the years, the Soo Line introduced thousands of Americans to Montreal and Quebec City, the famous Canadian Rockies resorts, and the city of Vancouver, the home port for CP's Pacific steamship services. The Soo also successfully competed on the Spokane and Portland routes from Minneapolis to the Pacific Northwest. In 1923 the "Soo Mountaineer" was launched, becoming the most famous and longest "two-nation" train journey in North America.