Premier Jean Charest's Liberals won a byelection in Quebec on Monday night, piling even more pressure on Parti Quebecois Leader Pauline Marois.

Liberal candidate Damien Arsenault stormed to victory in Bonaventure with about 50 per cent of the popular vote.

While the PQ was not expected to win a riding that has been Liberal for all but four of the last 55 years, Marois visited Bonaventure several times during the campaign in the hope of shoring up support for candidate Sylvain Roy.

The byelection was a test for Charest but also for Marois.

The Liberals have been lagging in the polls, while Marois has been unable to assert herself as leader and has been rocked by a wave of departures from the party this year.

In order to focus on the byelection, the PQ went as far as to postpone a party meeting scheduled for this past weekend.

But with opinion polls suggesting the PQ would get hammered in Bonaventure, Marois then declared the byelection was not a test of her leadership.

Both the Liberals and the PQ received a break of some sorts in the byelection because a newly formed party did not field a candidate.

Opinion polls indicate Coalition avenir Quebec, which is headed by former PQ cabinet minister Francois Legault, is way ahead of the Liberals and the PQ.

Bonaventure -- on the southern Gaspe Peninsula -- has been Liberal since 1956, except for a four-year PQ interlude between 1994 and 1998.

The byelection was held to replace former deputy premier Nathalie Normandeau, who resigned in September.

The victory gave the Liberals a 65th member in the 125-seat national assembly, compared with 45 for the PQ. The Action democratique du Quebec has four and Quebec solidaire one.

There are 10 Independents -- most of them who quit the PQ earlier this year because they were upset with Marois' leadership.

The PQ won Bonaventure in 1994 when the party formed the government under Jacques Parizeau.

Normandeau then grabbed it back for the Liberals with a narrow victory in 1998 before she romped to massive wins in 2003, 2007 and 2008.