The Province of Canada (or the United Province of Canada or the United Canadas) was a British colony in British North America from 1841 to 1867. Its formation reflected recommendations made by John Lambton, 1st Earl of Durham, in the Report on the Affairs of British North America following the Rebellions of 1837–1838.

The Act of Union 1840, passed on 23 July 1840 by the British Parliament and proclaimed by the Crown on 10 February 1841, merged the Colonies of Upper Canada and Lower Canada by abolishing their separate parliaments and replacing them with a single one with two houses, a Legislative Council as the upper chamber and the Legislative Assembly as the lower chamber. In the aftermath of the Rebellions of 1837–1838, unification of the two Canadas was driven by two factors. Firstly, Upper Canada was near bankruptcy because it lacked stable tax revenues, and needed the resources of the more populous Lower Canada to fund its internal transportation improvements. Secondly, unification was an attempt to swamp the French vote by giving each of the former provinces the same number of parliamentary seats, despite the larger population of Lower Canada.

Although Durham's report had called for the Union of the Canadas and for responsible government (a government accountable to an independent local legislature), only the first of the two recommendations was implemented in 1841. For the first seven years, the government was led by an appointed governor general accountable only to the British government. Responsible government was not achieved until the second LaFontaine–Baldwin ministry in 1849, when Governor General James Bruce, 8th Earl of Elgin, agreed that the cabinet would be formed by the largest party in the Legislative Assembly, making the premier the head of the government and reducing the governor general to a more symbolic role.

The Province of Canada ceased to exist at Canadian Confederation on 1 July 1867, when it was divided into the Canadian provinces of Ontario and Quebec. Ontario included the area occupied by the pre-1841 British colony of Upper Canada, while Quebec included the area occupied by the pre-1841 British colony of Lower Canada (which had included Labrador until 1809, when Labrador was transferred to the British colony of Newfoundland). Upper Canada was primarily English-speaking, whereas Lower Canada was primarily French-speaking.

The Province of Canada was divided into two parts: Canada East and Canada West.

Canada East was what became of the former colony of Lower Canada after being united into the Province of Canada. It would become the province of Quebec after Confederation.

Canada West was what became of the former colony of Upper Canada after being united into the Province of Canada. It would become the province of Ontario after Confederation.

The location of the capital city of the Province of Canada changed six times in its 26-year history. The first capital was in Kingston (1841–1844). The capital moved to Montreal (1844–1849) until rioters, spurred by a series of incendiary articles published in The Gazette, protested against the Rebellion Losses Bill and burned down Montreal's parliament buildings. It then moved to Toronto (1849–1851). It moved to Quebec City from 1851 to 1855, then returned to Toronto from 1855 to 1859 before returning to Quebec City from 1859 to 1865. In 1857, Queen Victoria chose Ottawa as the permanent capital of the Province of Canada, initiating construction of Canada's first parliament buildings, on Parliament Hill. The first stage of this construction was completed in 1865, just in time to host the final session of the last parliament of the Province of Canada before Confederation in 1867.

The Governor General remained the head of the civil administration of the colony, appointed by the British government, and responsible to it, not to the local legislature. He was aided by the Executive Council and the Legislative Council. The Executive Council aided in administration, and the Legislative Council reviewed legislation produced by the elected Legislative Assembly.

Sydenham came from a wealthy family of timber merchants, and was an expert in finance, having served on the English Board of Trade which regulated banking (including the colony). He was promised a barony if he could successfully implement the union of the Canadas, and introduce a new form of municipal government, the District Council. The aim of both exercises in state-building was to strengthen the power of the Governor General, to minimise the effect of the numerically superior French vote, and to build a "middle party" that answered to him, rather than the Family Compact or the Reformers. Sydenham was a Whig who believed in rational government, not "responsible government". To implement his plan, he used widespread electoral violence through the Orange Order. His efforts to prevent the election of Louis LaFontaine, the leader of the French reformers, were foiled by David Willson, the leader of the Children of Peace, who convinced the electors of the 4th Riding of York to transcend linguistic prejudice and elect LaFontaine in an English-speaking riding in Canada West.

Bagot was appointed after the unexpected death of Thomson, with the explicit instructions to resist calls for responsible government. He arrived in the capital, Kingston, to find that Thomson's "middle party" had become polarised and he therefore could not form an executive. Even the Tories informed Bagot he could not form a cabinet without including LaFontaine and the French Party. LaFontaine demanded four cabinet seats, including one for Robert Baldwin. Bagot became severely ill thereafter, and Baldwin and Lafontaine became the first real premiers of the Province of Canada. However, to take office as ministers, the two had to run for re-election. While LaFontaine was easily re-elected in 4th York, Baldwin lost his seat in Hastings as a result of Orange Order violence. It was now that the pact between the two men was completely solidified, as LaFontaine arranged for Baldwin to run in Rimouski, Canada East. This was the union of the Canadas they sought, where LaFontaine overcame linguistic prejudice to gain a seat in English Canada, and Baldwin obtained his seat in French Canada.

The Baldwin–LaFontaine ministry barely lasted six months before Governor Bagot also died in March 1843. He was replaced by Charles Metcalfe, whose instructions were to check the "radical" reform government. Metcalfe reverted to the Thomson system of strong central autocratic rule. Metcalfe began appointing his own supporters to patronage positions without Baldwin and LaFontaine's approval, as joint premiers. They resigned in November 1843, beginning a constitutional crisis that would last a year. Metcalfe refused to recall the legislature to demonstrate its irrelevance; he could rule without it. This year-long crisis, in which the legislature was prorogued, "was the final signpost on Upper Canada's conceptual road to democracy. Lacking the scale of the American Revolution, it nonetheless forced a comparable articulation and rethinking of the basics of political dialogue in the province." In the ensuing election, however, the Reformers did not win a majority and thus were not called to form another ministry. Responsible government would be delayed until after 1848.

Cathcart had been a staff officer with Wellington in the Napoleonic Wars, and rose in rank to become commander of British forces in North America from June 1845 to May 1847. He was also appointed as Administrator then Governor General for the same period, uniting for the first time the highest Civil and military offices. The appointment of this military officer as Governor General was due to heightened tensions with the United States over the Oregon boundary dispute. Cathcart was deeply interested in the natural sciences, but ignorant of constitutional practice, and hence an unusual choice for Governor General. He refused to become involved in the day-to-day government of the conservative ministry of William Draper, thereby indirectly emphasising the need for responsible government. His primary focus was on redrafting the Militia Act of 1846. The signing of the Oregon Boundary Treaty in 1846 made him dispensable.

Elgin's second wife, Lady Mary Louisa Lambton, was the daughter of Lord Durham and niece of Lord Grey, making him an ideal compromise figure to introduce responsible government. On his arrival, the Reform Party won a decisive victory at the polls. Elgin invited LaFontaine to form the new government, the first time a Governor General requested cabinet formation on the basis of party. The party character of the ministry meant that the elected premier – and no longer the governor – would be the head of the government. The Governor General would become a more symbolic figure. The elected Premier in the Legislative Assembly would now become responsible for local administration and legislation. It also deprived the Governor of patronage appointments to the civil service, which had been the basis of Metcalfe's policy. The test of responsible government came in 1849, when the Baldwin–Lafontaine government passed the Rebellion Losses Bill, compensating French Canadians for losses suffered during the Rebellions of 1837. Lord Elgin granted royal assent to the bill despite heated Tory opposition and his own personal misgivings, sparking riots in Montreal, during which Elgin himself was assaulted by an English-speaking Orange Order mob and the Parliament buildings were burned down.

It was under Head, that true political party government was introduced with the Liberal-Conservative Party of John A. Macdonald and George-Étienne Cartier in 1856. It was during their ministry that the first organised moves toward Canadian Confederation took place.

It was under Monck's governorship that the Great Coalition of all of the political parties of the two Canadas occurred in 1864. The Great Coalition was formed to end the political deadlock between predominantly French-speaking Canada East and predominantly English-speaking Canada West. The deadlock resulted from the requirement of a "double majority" to pass laws in the Legislative Assembly (i.e., a majority in both the Canada East and Canada West sections of the assembly). The removal of the deadlock resulted in three conferences that led to confederation.

Thomson reformed the Executive Councils of Upper and Lower Canada by introducing a "President of the Committees of Council" to act as a chief executive officer for the council and chair of the various committees. The first was Robert Baldwin Sullivan. Thomson also systematically organised the civil service into departments, the heads of which sat on the Executive Council. A further innovation was to demand that every Head of department seek election in the Legislative Assembly.

The Legislative Council of the Province of Canada was the upper house. The 24 legislative councillors were originally appointed. In 1856, a bill was passed to replace the process of appointing members by a process of electing members. Members were to be elected from 24 divisions in each of Canada East and Canada West. Twelve members were elected every two years from 1856 to 1862. Members previously appointed were not required to relinquish their seats.

Elections to the Legislative Assembly of the Province of Canada (1841–1863) – seats won by party

Year		1841			1844			1848			1851			1854			1858			1861			1863
		CW	CE	Total	CW	CE	Total	CW	CE	Total	CW	CE	Total	CW	CE	Total	CW	CE	Total	CW	CE	Total	CW	CE	Total
	Reform	29		29	12		12	23		23	20		20	19		19
	Clear Grits													14		14
	Radical Reform													6		6
	Moderate Reform																5		5	6		6	2		2
	Patriote		21	21		23	23		23	23
	Rouges											4	4		19	19		10	10
	Liberal					5	5		9	9		9	9				34	5	39	29	29	58	39	25	64
	Family Compact	10		10
	Tory		17	17	28	13	41	18	6	24	20	3	23
	Ministerialist											23	23		35	35
	Bleus																	33	33		27	27		25	25
	Liberal-Conservative													25	9	34	24	15	39	29	8	37	24	11	35
	Independent	3	4	7	2	1	3	1	4	5	1	4	5	1	2	3	2	2	4	2	1	3		4	4
Total		42	42	84	42	42	84	42	42	84	42	42	84	65	65	130	65	65	130	65	65	130	65	65	130