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Peggy Nash's NDP leadership bid on Tuesday received the endorsement of Pierre Ducasse, who wrote the party's Sherbrooke Declaration on conditions for Quebec secession. (Adrian Wyld/Canadian Press)

The principal author of the NDP's signature policy on Quebec has thrown his support behind Peggy Nash's bid to lead the federal New Democrats.

Pierre Ducasse, who sought the leadership himself in 2003, is endorsing the Toronto MP this time.

Ducasse ran a distant fifth in the contest that elected Jack Layton, who died of cancer last August.

He subsequently became Layton's senior adviser on Quebec and helped draft the so-called Sherbrooke Declaration.

The controversial declaration commits the NDP to accept a bare majority referendum vote as sufficient to trigger negotiations on Quebec's secession from Canada.

The Sherbrooke Declaration has been controversial elsewhere in Canada but is thought to have helped the NDP sweep 59 of Quebec's 75 seats in last May's election.

Nash says the declaration is mostly about Quebecers and Canadians working together.

"If you believe in Quebec’s right to self-determination you have to recognize that if Quebecers make a decision, if a majority of Quebecers make a decision, according to the Supreme Court that would enter into negotiations with the other provinces and the federal government," she said.

"It’s not about dividing people, it’s about bringing people together so that we can have a positive outlook, move forward in Canada instead of constantly saying we have to accept less and move backwards."

with a file from CBC News