Official Opposition (Canada) in the context of "Leader of the Official Opposition (Canada)"

The Legislative Assembly of Ontario (OLA; French: Assemblée législative de l'Ontario) is the legislative chamber of the Canadian province of Ontario. Its elected members are known as Members of Provincial Parliament (MPPs). Bills passed by the Legislative Assembly are given royal assent by the lieutenant governor of Ontario to become law. Together, the Legislative Assembly and Lieutenant Governor make up the unicameral Legislature of Ontario. The assembly meets at the Ontario Legislative Building at Queen's Park in the provincial capital of Toronto.

Ontario uses a Westminster-style parliamentary government in which members are elected to the Legislative Assembly through general elections using a "first-past-the-post" system. The premier of Ontario (the province's head of government) holds office by virtue of their ability to command the confidence of the Legislative Assembly, typically sitting as an MPP themselves and lead the largest party or a coalition in the Legislative Assembly. The largest party not forming the government is known as the Official Opposition, its leader being recognized as leader of the Opposition.

The 38th Canadian Parliament was in session from October 4, 2004, until November 29, 2005. The membership was set by the 2004 federal election on June 28, 2004, and it changed only somewhat due to resignations and by-elections, but due to the seat distribution, those few changes significantly affected the distribution of power. It was dissolved prior to the 2006 election.

It was controlled by a Liberal Party minority under Prime Minister Paul Martin and the 27th Canadian Ministry. The Official Opposition was the Conservative Party, led by Stephen Harper.

The Official Opposition Shadow Cabinet (French: Cabinet d'Ombre de l'Opposition Officielle) in Canada is composed of members of the main opposition party, His Majesty's Loyal Opposition, and is responsible for holding the Government to account and for developing and disseminating the party's policy positions. Members of the official opposition are generally referred to as opposition critics, but the term Shadow Minister (which is generally used in other Westminster systems) is also used.

The 2015 Canadian federal election was held on October 19, 2015, to elect the 338 members of the House of Commons of the 42nd Parliament of Canada. In accordance with the maximum four-year term under a 2007 amendment to the Canada Elections Act, the writs of election for the 2015 election were issued by Governor General David Johnston on August 4. At 11 weeks, the ensuing campaign was one of the longest in Canadian history: It was also the first time since 1979 that a prime minister attempted to remain in office into a fourth consecutive Parliament and the first time since 1980 that someone attempted to win a fourth term of any kind as prime minister. (In both cases, it was Pierre, Justin Trudeau’s father, who attempted in 1979 to win a 4th consecutive term and succeeded in 1980 in winning a fourth term overall.) This is also the most recent election in which a majority government was formed.

The Liberal Party won 184 seats, forming a majority government with its leader Justin Trudeau becoming prime minister. Trudeau and the rest of his cabinet were sworn in on November 4, 2015. The Conservative Party, led by incumbent Prime Minister Stephen Harper, won 99 seats, becoming the Official Opposition after nearly a decade on the government benches. The New Democratic Party, led by Tom Mulcair, won 44 seats, becoming the third-largest party in the House of Commons, after having formed the Official Opposition following the 2011 election. The Bloc Québécois won 10 seats, the Green Party won 1 seat, and Strength in Democracy lost all its seats.

The leader of the Official Opposition (French: chef de l'Opposition officielle) is the member of Parliament (MP) who leads the Official Opposition in Canada. This is typically the leader of the party possessing the most seats in the House of Commons that is neither the governing party nor part of a governing coalition.

Pierre Poilievre, MP for Battle River—Crowfoot, has been the leader of the Official Opposition since August 2025. Poilievre previously served in the role from September 2022 to April 2025, when he lost his seat in Carleton in the 2025 federal election. He was elected to his current seat in an August by-election, once again becoming leader of the Opposition.

The New Democratic Party (NDP; French: Nouveau Parti démocratique, NPD) is a federal political party in Canada. Widely described as social democratic, the party sits at the centre-left to left-wing of the Canadian political spectrum, to the left of the Liberal Party. The party was founded in 1961 by the Co-operative Commonwealth Federation and the Canadian Labour Congress. As of 2025, it is the fourth-largest party in the House of Commons, with seven seats, sharing the balance of power in the 45th Parliament.

The federal and provincial (or territorial) level NDPs are more integrated than other political parties in Canada, and have shared membership. The NDP has never won the largest share of seats at the federal level and thus has never formed a government. From 2011 to 2015, it formed the Official Opposition; apart from this, it has been the third or fourth-largest party in the House of Commons. However, the party has held the balance of power, and with it considerable influence, during periods of Liberal minority governments. Sub-national branches of the NDP have formed the government in six provinces (Ontario, Manitoba, Saskatchewan, Alberta, British Columbia, and Nova Scotia) and the territory of Yukon. The NDP supports a mixed economy, broader welfare, LGBTQ rights, international peace, environmental stewardship, and expanding Canada's universal healthcare system to include dental care, mental health care, eye and hearing care, infertility procedures, and prescription drugs.