The clash between the PQ leader and Legault, leader of the Coalition for Québec's Future, is the last of four consecutive debates featuring the province's political leaders.
Marois and Legault were to debate four topics: governance, social policy, the economy and the national question.
Marois kicked off the highly anticipated encounter by telling Quebecers that a PQ government elected on Sept. 4 would be clean.
"You have in front of you two very different visions of Quebec," she said. "My vision is to present an honest and responsible government. And we are going to do that with Quebecers."
With corruption a hot-button issue in the campaign, Legault didn't want to let his PQ rival occupy centre stage on the issue.
"I think what Quebecers want is a clean and efficient government that stands up to interest groups," Legault told viewers. "The priority in Quebec is a major cleanup to get rid of corruption and waste."
The clash between the two was expected to have some extra spice because of their past, which included five years together in the cabinets of Lucien Bouchard and Bernard Landry.
Marois was to make a run for the PQ leadership in 2001, but backed out after being abandoned by none other than Legault, who threw his support behind Landry.
The previous head-to-head debates this week saw Marois duelling with Liberal Leader Jean Charest on Monday, and Charest duking it out with Legault on Tuesday.
Quebecers go to the polls on Sept. 4.
One of the more interesting aspects of the Marois-Legault debate was to be their exchange on sovereignty referendums.
Marois is constantly vague on the timing of the next one, while Legault says he will not hold a referendum for 10 years and that he would even vote No if one were held right now.
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