David was declared the winner in Montreal's Gouin riding, while her cohort Amir Khadir retained his seat in Mercier.
David beamed at the standing-room crowd that was packed into Montreal's Olympia Theatre, where her victory party was held Tuesday night.
She thanked voters in her riding "from the bottom of my heart, for having the audacity to believe in me and believe in Québec Solidaire."
"Thank you for expressing a profound desire for a feminist, ecologist and sovereigntist change."
To a roar of cheers, David paid homage to her PQ rival.
"I'd also like to, as a feminist, to recognize the work of Pauline Marois, who will be Quebec's first premier." David vowed to support any PQ policy that "moves towards our social project, and support equality between men and women, and the environment."
She says she's wanted to be an MNA for years, to give voice to the voiceless.
QS matures as political party
David rose to the campaign challenge with a critically-acclaimed performance during the first televised campaign debate.
Observers called her performance likeable, even-keeled, sensible — and said she was a refreshing counterpart to the other main party leaders.
QS has made great strides as a political party since Khadir and David co-founded the left-leaning, sovereignty movement in 2006.
Khadir spent the first four years of his political career honing a reputation as a political maverick, and helped draw media attention to the party.
QS built momentum last spring by rallying with striking students in the tuition hike protests.
Bolstered by new donors and supporters, QS rolled out a bigger electoral machine in this election, calling on voters to stand up (with its slogan "Debout").
With a platform built on progressive, environmental and feminist principles, QS campaigned as an alternative to the Parti Québécois's controversial identity politics.
Popular support for QS shot up during the campaign, especially in downtown ridings on the island of Montreal.