The two politicians will meet in Montreal on Friday, according to Mulcair.
The encounter should prove interesting: the NDP surged to victory in 59 of Quebec's 75 ridings in the 2011 federal election, crushing the Bloc Quebecois, the Parti Quebecois' longtime ally.
The NDP leader said Tuesday he will listen attentively to Marois and help her in the future when he believes it is good for Quebecers as a whole.
''When I'm convinced that it's a matter that can interest all Quebecers, obviously she'll get support,'' Mulcair said in Quebec City where he was attending a convention of the Communications, Energy and Paperworkers Union.
But he also said such co-operation won't be forthcoming if he believes Marois is just out to prove that Canada can't work.
Mulcair said he would work on a case-by-case basis with Marois once he knows her intentions.
But Mulcair suggested he is sensitive to Quebec's particular demands given his political past in the province, which included a stint as environment minister.
Marois met with Prime Minister Stephen Harper in Africa last Saturday just before the opening of the summit of la Francophonie.