The Opposition Parti Quebecois retained two ridings in byelections Monday as Jean-Francois Lisee passed his first major test since becoming leader of the sovereigntist party two months ago.

The governing Liberals won their Montreal stronghold of Verdun but saw their share of the popular vote drop in all four byelections when compared with their performances in 2014.

One of the PQ victories came in Saint-Jerome, which had been vacant since former leader Pierre Karl Peladeau's resignation from politics last May.

Marc Bourcier had more than 45 per cent of the vote for the PQ, compared with the 36.8 per cent garnered by Peladeau in the 2014 election.

The PQ also kept Marie-Victorin, a Montreal-area riding last represented by the party's ex-house leader, Bernard Drainville. Catherine Fournier had more than 50 per cent of the vote, outdistancing Drainville's 38.2 per cent from two years ago.

"What a beautiful evening," Lisee said, pointing out that Fournier, at 24, is the youngest woman ever elected to the national assembly.

In another byelection Monday, Isabelle Melancon won Verdun for the Liberals with about 35 per cent of the popular vote, a significant drop from Jacques Daoust's 50.6 per cent two years ago.

Premier Philippe Couillard stood beside Melancon in Verdun and thanked volunteers and the candidates in the three other ridings.

"Of course we would have preferred different results but there will be other battles," he said. "We will continue our work. Our priorities remain the same: education; health, particularly the elderly; and of course jobs and the economy."

The fourth byelection of the night saw Eric Lefebvre of the Coalition for Quebec's Future easily win Arthabaska, which had been vacant since Sylvie Roy's death earlier this year.

Roy won the riding for the Coalition with a hefty majority in 2014 before she became an Independent a year later.

The results will have little impact on the standings in the 125-member legislature. The Liberals have 70 seats, the PQ 30 and the Coalition 21. There also three Quebec solidaire members and one Independent.

The next general election is set for the fall of 2018.