The youngest sitting member of the Parti Québécois has quit caucus to sit as an independent, sovereigntist MNA.

Catherine Fournier says she wants to build a non-partisan consensus between Quebecers who want to achieve independence, and that the movement is too fractured to achieve its goal under any of the existing parties.

The PQ is past the point where it can be saved by new leadership, she said.

"Even if the Parti Québécois eventually reforms itself, I believe that it's too late," she said at a news conference in her home riding of Marie-Victorin, which covers part of Montreal's South Shore.

She said her former party lacks the credibility and confidence of the public to be the vessel of the sovereignty movement on its own, and that it has been in decline since the 1995 referendum loss.

At 26 years old, Fournier is the youngest MNA in the National Assembly.

No plan to form new party

Fournier leaving the caucus also means the PQ falls to fourth place in number of seats in the National Assembly.

Québec Solidaire, which also has the goal of an independent Quebec as part of its platform, has 10 seats in the provincial legislature.

She will return to the National Assembly as independent, and says she has no plans to start her own party.

"The last thing that the sovereigntist movement needs today is a new sovereigntist political party," she said.

Instead, she said work must be done to create a sovereigntist network across partisan lines and include young people in the conversation.

Fournier said the PQ has known she was reflecting on her future since her re-election in October, and that her decision should come as no surprise to the party.

The party received just over 17 per cent of the popular vote in that election, one of its worst-ever showings. Even then-leader, Jean-François Lisée, lost his seat to QS.

Interim PQ leader Pascal Bérubé had a different take from Fournier's, saying the caucus was "shocked" by the news of her departure.

"We learned at the same time as you," he told journalists on Monday afternoon.

Bérubé said the party is in an "unprecedented" moment of reflection, where everything is on the table — as long as sovereignty remains at the heart of its platform.

He also questioned whether Fournier could be a legitimate representative of her voters, given that she is leaving the PQ just five months after running under its banner.

Fournier responded on Twitter, saying Bérubé's reaction is emblematic of the party's problems.

La réaction du Parti Québécois exprimée par son chef intérimaire Pascal Bérubé est à elle seule une bonne démonstration de ce qui ne fonctionne plus dans ce parti. <a href="https://twitter.com/hashtag/polqc?src=hash&ref_src=twsrc%5Etfw">#polqc</a> —@CathFournierQc

In a statement, Québec Solidaire wished Fournier luck in her endeavour, but added that it believes QS is the right party to make Quebec a country.

It pointed to its merging with the hardline party Option Nationale ahead of last fall's election as proof it can be the home for the province's sovereigntists.