A fourth MP of the current Canadian parliament has defected to join the Liberals, bringing Prime Minister Mark Carney closer to a majority in the House of Commons.

Lori Idlout, a member of the left-leaning New Democrats (NDP), is joining the governing party. In a statement issued by the Liberals, she said she had undergone "much personal reflection and encouragement from my community, family, and supporters".

Interim NDP leader Don Davies said he was "very disappointed", adding: "We believe that when someone rejects the decision of their electors and wants to join another party, they should put that decision to their voters."

The Liberals said they were "deeply excited to welcome" Idlout.

Idlout was first elected as an MP from the Canadian territory of Nunavut in 2021.

In its statement, the Liberal Party said she is "well known as a tireless champion for Nunavut".

"We are looking forward to working with her on our priorities, including addressing the high cost of living and improving the lives of Nunavummiut," the party said.

Idlout said that she believed her northern community needed "a strong and ambitious government", citing concerns about Canada's sovereignty, climate change and affordability.

"At this turning point in our history, I am ready to work with (Carney) to build a strong future for Nunavut and for all of Canada," Idlout said.

She told the CBC in January that she had been asked to consider joining the Liberals but was not yet ready to make the move.

Carney, who leads a minority government, has been closing in on a majority in recent months - largely helped by recent defections by three former Conservative members of parliament.

In February, Matt Jeneroux, a Conservative from Edmonton, joined the Liberal caucus. Two other Conservative MPs, Chris d'Entremont of Nova Scotia and Michael Ma of Ontario, had crossed the floor late last year to join Carney's government.

Opposition Conservatives have accused the Liberals of using "pressure tactics" on their members.

Over the weekend, Carney also announced three by-elections on 13 April - races that could secure the Liberals the majority government that they crave.

Two of the by-elections will be held in Toronto, in constituencies that are considered Liberal strongholds. The third will be a closely-watched contest in Montreal that his party won by just one vote in the last election - a result that was nullified by the Supreme Court.

If the Liberals win all three seats in April, following the addition of Idlout, they would secure 173 seats in the House of Commons, allowing the prime minister to likely avoid an election for three more years.

In the federal election a year ago, the NDP won just seven seats after losing significant vote share to rival parties.

The NDP will vote for a new leader later this month.