One of the ridings was Jean-Talon, a Quebec City constituency the Liberals have held since 1966.
Sebastien Proulx easily won, getting nearly 42 per cent of the votes, compared with the 44.5 per cent garnered by Yves Bolduc in the 2014 general election.
The PQ's Clement Laberge finished second behind Proulx with 30 per cent.
The other byelection in the provincial capital saw one former TV reporter, Veronyque Tremblay, defeat ex-journalist Jocelyne Cazin, who was running for the Coalition for Quebec's Future.
Tremblay snagged 41 per cent of the vote in Chauveau to emerge victorious with a majority of more than 1,900 votes. Cazin received between 33 and 34 per cent.
In comparison, the Coalition's Gerard Deltell won the riding in 2014 with 52.4 per cent of the vote and a majority of nearly 10,000 over the Liberal candidate.
Deltell stepped down earlier this year after announcing he will run for the federal Conservatives in the fall election.
Coalition Leader Francois Legault attempted to put a brave face on the setback in Chauveau.
"Our cause is good," he said. "Our cause is worth being fighted. We are going to continue our fight. We are going to continue to try to get Quebec back on track."
Late in the Chauveau campaign, the PQ sent in Peladeau's longtime partner and well-known TV personality, Julie Snyder, to boost the chances of candidate Sebastien Couture.
He ended up with just more than 15 per cent of the vote.
The results will have little impact on the makeup of the national assembly: the Liberals now have 71 of the 125 seats, compared with the PQ's 30, the Coalition's 21 and Quebec solidaire's three.
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