CAQ Leader François Legault on Sunday introduced his star candidate in the riding of St-Jérôme, a Laurentians town where Duchesneau has long lived.
The former Montreal police chief and whistleblower said he decided to join the political fray to fight corruption from the inside rather than the sidelines.
"I'm a fighter. Let the fight begin," he said. "I'm just asking the population, give us the tools to do it."
Duchesneau was hired by the Liberals in 2010 to investigate allegations of corruption and collusion in the construction industry.
His report, which he leaked to the media, included charges of illegal schemes in the construction industry and political financing.
Duchesneau was later called to testify at the Charbonneau Commission on corruption, where he revealed more shocking details about his allegations. The commission is on hiatus until mid-September, after voters go to the polls.
The timing of Liberal Leader Jean Charest's election call is disgraceful, Duchesneau said.
"What is a total disgrace as far as I'm concerned, is that knowing that the Charbonneau Commission is going to disclose important things that people need to know, before they cross an x on the ballot box, that we call an election prior to that. That's what upset me."
The Sunday morning announcement gave CAQ an immediate boost in credibility as it tries to make the fight against corruption a key issue for voters.
CAQ Leader Legault called Duchesneau "Quebec's Eliot Ness," and said it takes courage to tackle corruption.
"We think you need courage, and we think we're the only ones who can do it," said Legault, who smiled broadly throughout the news conference.
"The Parti Québécois, they have their hands tied with unions and groups. The Liberals have their hands tied with friends of the Liberal Party, we know that."
Liberal actions 'speak for themselves'
At a news conference following the announcement, Charest said his government has already taken steps to tackle corruption and illegal political financing, including calling an inquiry.
He pointed to several new laws introduced by his government aimed at addressing the issue.
He says his government implemented all 52 changes recommended in Duchesneau's report, and has introduced several laws aimed at addressing the issue.
"I think these actions speak for themselves," he said.
Charest said even Duchesneau, in a follow-up, praised his government's efforts. "He says we're going in the right direction, again. He says we're determined. And it goes on! Well, there's the answer of the Jacques Duchesneau before being a candidate, and the Jacques Duchesneau after becoming a candidate."
Charest has given his government an eight out of ten in dealing with the problem. Duchesneau said he was shocked when he heard Charest's assessment, and told reporters he would have given Charest a two out of ten.
PQ also fights corruption: Drainville
Parti Québécois Leader Pauline Marois skirted Duchesneau's candidacy, and let her right-hand man defend the party's record.
"Mr. Duchesneau doesn't have a monopoly on virtue," said PQ candidate Bernard Drainville.
"It's the Parti Québécois that asked the most questions about scandals in Mr. Charest's government, It's the Parti Québécois that brought to light the daycare scandal involving Mr. Tomassi and company, it's the Parti Québécois that proposed to limit political contributions to 100 dollars."
Duchesneau could just as easily joined the PQ "If he wanted to fight against corruption, and for integrity," Dranivlle said.