Canada’s ruling Liberals have edged closer to a majority government after a Conservative lawmaker crossed the floor, in yet another blow to the struggling Tories.

Rookie lawmaker Michael Ma said late on Thursday that he had decided to leave the Conservative party, for “the steady, practical approach” of prime minister Mark Carney’s government, which he said would “deliver on the priorities I hear every day, including affordability and the economy”.

He added: “After listening carefully to the people of Markham–Unionville in recent weeks and reflecting with my family on the direction of our country, I have informed the speaker and the leader of the opposition that I will be joining Prime Minister Mark Carney in the government caucus. This is a time for unity and decisive action for Canada’s future.”

Ma made the announcement the day after attending the Conservative Christmas party and posing for a photo with Tory leader Pierre Poilievre. He then attended a party hosted by the Liberals the next evening, appearing on stage with Carney to raucous applause.

The Liberals now have 171 seats in parliament: one short of a majority.

In a statement on social media, Poilievere said Ma “chose to endorse the very policies he was elected to oppose” and would join a party that was increasing the cost of living. “The people he let down the most are the ones who elected him to fight for an affordable future. He will have to answer to them.”

The crossing will sting the Conservatives, who have now lost three lawmakers. One crossed to the Liberals in November and another said he would resign in the coming months.

On Friday, government house leader Stephen MacKinnon said he believed there were more frustrated opposition members who might be tempted to defect to the Liberals.

“All of my colleagues here have the same experience of speaking to Conservative members, unfortunately a group which is in the minority in their group, who are extremely frustrated with the leadership of their party,” he said during a press conference, adding members were forced to participate in a “charade of obstruction” in order to oppose the Liberals that is “soul-destroying experience for many Conservative[s]”.

While the addition of a new member to caucus has buoyed Liberals, Carney has faced discontent within his own party.

Earlier this month, a prominent cabinet minister, Steven Guilbeault, resigned from his post, protesting Carney’s decision to support a controversial oil pipeline from Alberta to the Pacific Ocean.

Guilbeault, a longtime environmental advocate, warned the pipeline to the west coast “would have major environmental impacts … contribute to a significant increase in climate pollution, and move Canada further away from its greenhouse gas reduction targets”. Guibeault warned that lifting the moratorium on oil tanker traffic would significantly increase the risk of accidents in the region.