Unofficial results from Elections Canada on Tuesday showed Poilievre had easily won a by-election on Monday in the electorate of Battle River-Crowfoot in the western Canadian province of Alberta, a Conservative stronghold.
Poilievre, who accuses the Liberal government of botching its handling of US relations, will be able to confront Carney when the House of Commons returns on September 15.
Carney, who took over as prime minister in March, secured a strong minority government in April's federal election, while Poilievre lost the Ottawa-area seat he had held for 21 years.
Carney won on a promise to stand up to US President Donald Trump but has since moderated his approach even as Washington imposed more tariffs.
"Mark Carney has been failing. He's failed, he's backed down, he's made concession after concession vis-a-vis the Americans," Poilievre told a media conference last Thursday.
Carney, however, is in no immediate danger politically.
Although the Liberals fell three seats short of a majority in April, they should be able to rely on the support of smaller parties to survive confidence votes.
A Nanos Research poll earlier this month put the Liberals at 44 per cent popular support compared with 33 per cent for the Conservatives.
Carney had pulled the Liberals more to the centre and Poilievre would find it harder to draw a sharp contrast, said pollster Nik Nanos, CEO of Nanos Research.
"Poilievre needs to articulate what he learned from the last federal election and how his government would be different than a Carney government," he said via email.
At the start of the year the Conservatives looked set for a crushing election victory over the Liberals of then-Prime Minister Justin Trudeau, who were far behind in polls after more than nine years in power.
But Liberal fortunes soared after Trudeau announced he was stepping down and Trump began threatening Canada with tariffs and annexation.
Poilievre secured about 80 per cent of the vote, according to Elections Canada.
