Andrew Scheer says he is stepping down as Conservative leader as soon as a successor can be chosen.
Scheer addressed the House of Commons briefly at about noon Eastern time, saying leading his party had been the honour of his life but that he could not commit to giving the Conservatives 100 per cent any longer.
He called resigning "one of the most difficult decisions I have ever made."
"Serving as the leader of the party that I love so much has been the opportunity and the challenge of a lifetime," he said.
Prime Minister Justin Trudeau responded by saying he and Scheer, as well as the other parents in the House, share the goal of wanting to improve things for their children.
"We are politicians, we are in this House not in spite of having kids but because we have kids and are dedicated to building a better world for them with everything we have. And I respect that deeply in him," Trudeau said.
He said few know the challenges and rewards of leading a diverse party like the Conservatives or the Liberals.
He congratulated Scheer for showing "tremendous strength and compassion as he has done that through tragedies, difficulties, victories and more challenging moments."
Trudeau concluded by thanking Scheer "deeply for his service to Canada."
New Democrat Leader Jagmeet Singh said he wanted to acknowledge the "hard work" that Scheer has put into his various roles. Before leading the Conservatives, Scheer was Speaker of the House of Commons.
"I think we speak as a united voice in acknowledging that and thank you for your service," Singh said.
Ontario Premier Doug Ford thanked Scheer for his work as leader of the federal Conservatives.
"I wish Andrew Scheer all the best as he undertakes this new chapter in his life, and thank him for his service as the head of Her Majesty's Loyal Opposition and leader of the Conservative party," Ford said in a statement.
The decision comes less than two months after a disappointing election result and after weeks of Conservative infighting about whether Scheer should stay on.
Several prominent Conservatives have called outright for his resignation, or for him to re-apply for his job in a new leadership contest. Having not won power in October, he faced a mandatory leadership review in April.
Scheer was elected as the Tory leader in May 2017, barely besting Maxime Bernier in the contest after numerous rounds of voting.
The Conservatives held the Liberals to a minority government in October but many in the party had hoped for a better result.
Scheer was emotional in his seven-minute speech to the House of Commons, interrupted multiple times by applause and standing ovations from his caucus. His wife Jill was in the gallery watching.
Scheer said he has asked the Conservative national council to begin a leadership contest and that whoever wins the job will get his complete support.