On December 5, Elections Canada announced a by-election for the House of Commons will be held for the seat for Chicoutimi–Le Fjord (Quebec). The seat was vacated by MP Denis Lemieux, who announced his plan to resign in November for family reasons.

On December 4, Stéphane Perrault, Acting Chief Electoral Officer of Canada, received official notice from the Speaker of the House of Commons that the seat was vacant. Canadian law requires the date of this by-election be announced between December 15, 2017, and June 2, 2018, which will signal the start of the by-election period.