The history of the Canadian Army, began when the title first came into official use in November 1940, during the Second World War, and is still used today. Although the official titles, Mobile Command, and later Land Force Command, were used from February 1968 to August 2011, "Canadian Army" continued to be unofficially used to refer to the ground forces of the Canadian Armed Forces, much as it has been from Confederation in 1867 to the present. The term was often even used in official military publications, for example in recruiting literature and the official newspaper of the Canadian Forces, The Maple Leaf. On August 16, 2011, the title, "Canadian Army", was officially restored, once again bringing the official designation in line with common and historical usage.

Prior to Canadian Confederation in 1867, defence for the colonies that comprise present-day Canada was dependent on the armies of colonial powers. The military of New France (1608–1763) was dependent on the French Royal Army. Conversely, the defence of the English/British colonies of Newfoundland (1610–1907), and Nova Scotia (1654–1867) was dependent on the English/British Army. After the British conquest of New France in 1760, defence for the French colony of Canada (present-day Ontario, and Quebec), and St. John's Island was also reliant on the British Army. Both the British and French armies were augmented by locally recruited regulars, fencibles, and the Canadian militia. Many of these units were activated in times of war, but remained inactive in between.

During the War of 1812, locally raised Canadian units, including fencibles, and militia units from the Canadas, New Brunswick, Newfoundland, and Nova Scotia served alongside regular units of the British Army. These fencible and militia units played an instrumental role during the conflict. The history and heritage, as well as the War of 1812 battle honours awarded to many of these units, are perpetuated by current units within the Canadian Army.

While Canada developed a volunteer militia force of partially trained and often unpaid amateurs, defence of the country was dependent on a contingent of regular British soldiers, as well as naval defence through the Royal Navy. The Canadian Militia evolved from the various British garrison forces on the North American continent in the 19th century. In 1854, with the outbreak of the Crimean War, virtually the entire British garrison was pulled out of British North America to fight against Russia, and with many American politicians saying this was the opportune moment for the United States to realize its "manifest destiny" by annexing British North America, the government of the United Canadas, consisting of Canada West (modern Ontario) and Canada East (modern Quebec) passed the Militia Act of 1855 to create an active militia that was essentially a professional army, through not labelled as such. The "active militia" consisted of 5,000 men. The Canadian Army is a direct descendant of the "active duty militia" force created in 1855. Upon Canadian Confederation in 1867, the ground forces in Canada continued to be referred to as the Militia. Using the "active duty militia" of the United Canadas as its core, Parliament passed the Militia Act of 1868 merging the militias of New Brunswick and Nova Scotia into the militia of the United Canadas. In February 1869, the Defence minister, Sir George-Étienne Cartier, told the House of Commons that the Militia had 37,170 men under arms and 618,896 in reserve.

The primary action that the newly formed militia saw was from the Fenians, a group of Irish radicals who made several attempts in the late 19th century to invade some parts of southern Canada from the United States. The period of the Fenian raids in the 1860s and early 1870s was the peak of the efficiency of the Canadian militia. In 1866, at the Battle of Ridgeway the Fenians defeated the Canada West militia owing to the inexperience of the militiamen, but in 1870 the Quebec militia drove back the Fenians at Trout River and Eccles Hill with little trouble. In 1869, Canada purchased for $1.5 million the vast proprietary colony of Rupert's Land run by the Hudson's Bay Company that comprised all of northern Quebec, northern Ontario, Manitoba, Saskatchewan, Alberta, the Yukon, the Northwest Territories, and Nunavut. The 10,000 people, many of them Métis in the Red River Colony in what is now southern Manitoba, were not consulted about the sale, and under the leadership of Louis Riel rebelled, setting up a provisional government to negotiate their admission to Confederation. Donald Smith of the Hudson's Bay Company had been appointed to negotiate with Riel by Ottawa and arranged a settlement under which Canada would create a new province called Manitoba in exchange for the Métis laying down their arms. However, the execution of Thomas Scott, an Orangeman from Ontario, by the Métis, created much fury in Ontario, a province where the Loyal Orange Order was a major political force. To placate voters in Ontario, an expedition was sent to down the Red River Rebellion. In 1870, an Anglo-Canadian force consisting of the 400 men from British King's Royal Rifle Corps with the rest being Ontario militiamen, consisting of 1,044 men in total under the command of General Garnet Wolseley made a gruelling march across northern Ontario to the Red River colony. Riel fled and the rebellion ended without any fighting, and the terms already agreed upon between Smith and Riel were implemented with Manitoba becoming the 5th province.

After the Treaty of Washington (1871) and the end of the Fenian raids, the British began to downsize their garrisons in Canada, mainly to move troops to other areas of the Empire, but also due to friendlier relations with the United States, Canada's immediate neighbour, and the only country capable of launching an armed invasion of the country. In 1871, the British garrisons in Canada were almost completely pulled out with British garrisons remaining only in Halifax and Esquimalt. After 1871, the responsibility for the defence of Canada rested with the Dominion government.

This led to the designation of a Permanent Active Militia as the regular army of Canada (regular in the sense that they were full-time professional soldiers) and the Non-Permanent Active Militia (or reserves, part-time soldiers with vocations in the civilian world who trained on evenings, weekends, and for short periods in the summer months). The Canadian historian René Chartrand wrote: "The government's traditional policy was to spend as little as possible on defence while keeping up a basic military force". As maintaining the non-permanent active militia was the cheapest option, this was the one that Ottawa pursued.

In 1876, the Royal Military College was founded to train officers for the Permanent Active Militia. Owing to the lack of officers, British Army officers continued to be seconded to serve as the senior commanders of the militia. 'A' and 'B' Batteries of Garrison Artillery were formed as the first units of Canada's permanent military force in 1871 in Kingston and Quebec City respectively, with a third ('C' Battery) authorized in 1883 and formed in 1887 in Esquimalt. These batteries are now incorporated in the 1st Regiment Royal Canadian Horse Artillery. The Cavalry School Corps, which eventually became The Royal Canadian Dragoons, and the Infantry School Corps, which became The Royal Canadian Regiment, were both formed on 21 December 1883.