On February 25, three by-elections will be held to fill vacancies in the Canadian House of Commons. The by-elections will take place for the electoral districts of Burnaby South (British Columbia), Outremont (Quebec) and York–Simcoe (Ontario).

The seat for Burnaby South (British Coumbia) became vacant following the resignation of Kennedy Stewart, who resigned on September 14 in order to run for mayor of Vancouver.

The seat for Outremont (Quebec) became vacant following the resignation of Tom Mulcair, who left office to teach at the at Universite de Montreal and to become a regularly scheduled political commentator at CJAD radio and CTV news.

The seat for York–Simcoe (Ontario) became vacant following the resignation of Peter Van Loan, who resigned on September 30 to return to the practice of law.

Sometime before January 30, 2019, a by-election will be announced for the seat in the House of Commons representing Outremont in the province of Quebec.

On August 3, the Chief Electoral Officer of Canada, Stéphane Perrault, received official notice from the Speaker of the House of Commons that the seat for Outremont (Quebec) became vacant following the resignation of Tom Mulcair, who left office to teach at the at Universite de Montreal and to become a regularly scheduled political commentator at CJAD radio and CTV news.

Under the law, the by-election date must be announced between August 14, 2018, and January 30, 2019, and will signal the start of the by-election period. According to Elections Canada, the earliest date the by-election can be held is September 24, 2018.