Provisional results showed the predominantly French-speaking province of nine million had opted for the Parti Quebecois of Paul St-Pierre Plamondon, who is promising to hold a referendum on breaking from Canada once Trump leaves office.
"A referendum is a chance to decide things for ourselves ... our national destiny will be achieved one day," Plamondon, a 49-year-old former lawyer, told cheering supporters on Monday.
But he faces challenges, since the PQ only won 59 of the 127 seats in the Quebec national assembly, or five short of a majority.
The legislature must approve a referendum vote.
Plamondon conceded he would need support from opposition parliamentarians to proceed.
The widely expected result reflected voter fatigue with the centre-right Coalition Avenir Quebec government, in office since 2018, analysts said.
The CAQ lost all its 79 seats.
Carney, who has stressed the need for a united front to tackle Trump's tariffs, must now work with a Quebec premier who is determined to break up Canada.
In addition, the energy-rich province of Alberta will hold a non-binding vote this month on whether its residents want independence.
Independence votes held by previous PQ governments in 1980 and 1995 failed, and polls indicate support for the idea of breaking with Canada is at 30 per cent, near record lows.
Plamondon, citing the political uncertainty and economic damage done by the tariffs, says he will not call another referendum until Trump is out of White House.
In remarks addressed to Carney, Plamondon said he would defend Quebec's interests above all, but reiterated that he was happy to work with Ottawa whenever it suited Quebec.
Despite the unclear referendum prospects, some PQ policies look set to boost tension with Ottawa, however.
The party plans to resist any federal bid to boost immigration, cut Quebec's ties to the British monarchy and block a proposed high-profile high-speed rail link with Ontario.
Carney congratulated Plamondon on X, saying, "Building a stronger Quebec is core to our mission of building a stronger Canada."
Carney looked forward to working with Plamondon to support Quebec's businesses and workers hit by tariffs, he said.
The PQ - which benefited significantly from vote-splitting between the five major parties in the fray - took just 28 per cent of the vote, the lowest share of ballots ever captured by a winning party in Quebec electoral history.
The CAQ's collapse reflects the fact that politics in Quebec is traditionally more volatile than elsewhere in Canada.
The PQ jumped from seven seats to take power.
