Carney's win represented a repudiation of Trump's volley of threats to annex Canada and make it the "51st state." That rhetoric – along with punishing tariffs on Canadian goods – has sparked an unprecedented wave of Canadian nationalism and overturned years of stability between the two neighbors.

With the vote count incomplete, it was unclear whether Mr. Carney’s Liberal Party would secure a majority in Parliament. Pierre Poilievre, the opposition leader, lost his seat.