Grand Trunk Railway of Canada was built to provide a main trunk line "throughout the entire length of the Province of Canada, and from the eastern frontier thereof ... to the city and port of Halifax." Under the sponsorship of Sir Francis Hincks, the GTR was formally incorporated in 1852 to build a railway from Toronto to Montréal. In 1853 it amalgamated with 5 other railway companies, a method of operating which was to characterize its major expansion periods and supplement the construction of new track. Much of the financing had to be raised in England, and the English construction firm of Peto, Brassey, Jackson and Betts received the contract to build the Montréal-to-Toronto section in return for agreeing to promote the company. Gzowski & Company received the contract for the Toronto-to-Sarnia section. Brassey claimed his company suffered heavy losses on its contract, while Casimir Gzowski, more familiar with Canadian conditions, made a fortune. Hincks's enemies claimed that he, too, made a fortune - at the expense of the railway.

Work proceeded vigorously from town to town. Navvies from England swelled the labour force - at one time 14 000 men and 2000 horses were employed in Canada West alone. The line did not face challenges such as those of the Canadian Pacific Railway in the mountains but achieved at least one notable engineering feat in construction of the tubular Victoria Bridge across the St Lawrence R at Montréal. The 2009 m long iron tube rested on 2 abutments and 24 piers designed to resist the crushing ice of the river; it was opened to traffic in Dec 1859. Despite financial difficulties, the GTR expanded steadily, often leasing existing railways as a means of expansion. It eliminated its main competitor and added another 1450 km of track with the takeover of the Great Western Railway in 1882. Additional links to the US rail system were established with the International Bridge across the Niagara R, and the impressive St Clair Tunnel beneath the St Clair R. At Confederation the GTR was the largest railway system in the world, with 2055 km of track; by the late 1880s it had grown to over 700 locomotives, 578 cars, 60 post-office cars, 131 baggage cars, 18 000 freight cars and 49 snowplows. The GTR ran unbroken from Sarnia to Portland, Maine.

Cost of construction, absentee management (the head office was in London, Eng) and failure to generate anticipated levels of traffic left the company debt ridden and unable to upgrade its equipment. It suffered bad publicity with several accidents; on 29 June 1864 a GTR train plunged off the Beloeil Bridge into the Rivière Richelieu, killing 99 people. Another incident made headlines around the world when, on 15 Sept 1885, a GTR train was charged by Jumbo, the famous circus elephant, near St Thomas, Ont. The elephant was killed. From the mid-1890s until WWI the GTR undertook a massive betterment program on its property. This included double-tracking of the main line from Montréal to Sarnia, reducing curves and grades to improve operating efficiency, and reconstruction of bridges, buildings and yards. Subsequent rebuilding of the system was not required until after WWII.

Envious of the CPR thrust into the West, the GTR set up a subsidiary, the Grand Trunk Pacific, to build a transcontinental line. Completed in 1914, the railway was a financial disaster and was largely responsible for the bankruptcy of the GTR in 1919. The federal government, which had already given the GTR some $28 million in subsidies and loans, took over the railway on 10 Oct 1919. It was placed under the management of the Canadian National Railways on 30 Jan 1923.