Gabriel Nadeau-Dubois, a former student leader and Québec Solidaire's co-spokesperson, will represent the Montreal riding of Gouin in the National Assembly.

Nadeau-Dubois won in a landslide, with 69 per cent of the vote. None of the other 12 candidates received more than 10 per cent.

"It's unbelievable. It's very humbling. And I'm deeply thankful to the electors for that," Nadeau-Dubois said after his victory.

"I'm also aware that it's a big responsibility."

With the victory, Québec Solidaire, a left-wing, sovereignist party, now has three seats in the National Assembly. It has been embroiled in controversy in recent weeks for shooting down a proposed strategic alliance with the Parti Québécois.

Nadeau-Dubois said social housing and improved funding for education would be two priorites for his riding, which has 44,000 eligible voters.

​Quebec Liberal Party candidate Jonathan Marleau received 8.9 per cent and Option Nationale's Vanessa Dion received 7.86 per cent. The Parti Québécois did not have a candidate in the race.

The participation rate was 32.7 per cent.

The byelection was called after Françoise David of Québec Solidaire announced in January that she was leaving politics.