The United Church of Canada (UCC; French: Église unie du Canada, abbreviated EUC) is a mainline Protestant denomination that is the largest Protestant Christian denomination in Canada and the second largest Canadian Christian denomination after the Catholic Church in Canada.

The United Church was founded in 1925 as a merger of four Protestant denominations with a total combined membership of about 600,000 members: the Methodist Church (Canada), the Congregational Union of Ontario and Quebec, two-thirds of the congregations of the Presbyterian Church in Canada, and the Association of Local Union Churches, a movement predominantly of the three provinces of the Canadian Prairies. The Canadian Conference of the Evangelical United Brethren Church joined the United Church of Canada on January 1, 1968.

Membership peaked in 1964 at 1.1 million. From 1991 to 2001, the number of people claiming an affiliation with the United Church decreased by 8%, the third largest decrease among Canada's large Christian denominations. In 2011, Statistics Canada reported approximately 2 million people identifying as adherents. The 2021 Canadian census found that 1.2 million Canadians (3.3% of the population) self-identified with the church, remaining the second-largest Christian denomination in Canada. Church statistics for the end of 2023 showed 2,451 congregations and 325,315 members in 243,689 households under pastoral care, of whom 110,878 attend services regularly.

The United Church has a "council-based" structure, where each council (congregational, regional, or denominational) has specific responsibilities. In some areas, each of these councils has sole authority, while in others, approval of other councils is required before action is taken. (For example, a congregation requires regional council approval before a minister can be called or appointed to the congregation.) The policies of the church are inclusive and liberal: there are no restrictions of gender, sexual orientation or marital status for a person considering entering the ministry; interfaith marriages are recognized; communion is offered to all Christian adults and children, regardless of denomination or age.^{[page needed]}

In the early 20th century, the main Evangelical Protestant denominations in Canada were the Presbyterian, Methodist and Congregational churches. Many small towns and villages across Canada had all three, with the town's population divided among them. Especially on the prairies, it was difficult to find clergy to serve all these charges, and there were several instances where one minister would serve his congregation, but would also perform pastoral care for the other congregations that lacked a minister. On the prairies, a movement to unite all three major Protestant denominations began, resulting in the Association of Local Union Churches.

Facing a de facto union in the western provinces, the three denominations began a slow process of union talks that eventually produced a Basis of Union.

However, not all elements of the churches involved were happy with the idea of uniting under one roof; a substantial minority of Presbyterians remained unconvinced of the virtues of church union. Their threat to the entire project was resolved by giving individual Presbyterian congregations the right to vote on whether to enter or remain outside the United Church. In the end, 302 (6.7%) out of 4,509 congregations of the Presbyterian Church (211 from southern Ontario) chose to reconstitute themselves as a "continuing" Presbyterian Church in Canada.

The United Church of Canada is an amalgamation of the Union of Methodist, Presbyterian and Congregational churches.