It's support he could likely do without, given that his political opponents have launched repeated attacks against Couillard for his ties to Porter.
From behind the walls of a Panamanian jail, Porter told his biographer last weekend he still considers Couillard a friend and believes he would make a good premier.
Author Jeff Todd said he interviewed the controversial ex-hospital administrator about his relationship with Couillard, who's vying to win the premier's chair from Parti Quebecois Leader Pauline Marois in next Monday's election.
"I do think he would make a good first minister," Porter said of Couillard in a transcript of the conversation posted online Wednesday.
"One thing about Philippe is he is extremely intelligent, versatile and he has a good world understanding. He understands Quebec, Canada and the world."
Todd said Porter called him from La Joya prison, where he is being detained while fighting extradition to Canada. He is facing fraud charges related to a $1.3-billion hospital project in Montreal.
With less than a week to go before the election, Porter's endorsement surfaced at a particularly sensitive time for Couillard, who has been haunted by his connections to the disgraced administrator.
The two set up a company together in 2010, but the Liberal leader has said no business was ever conducted and that there were no financial statements before the firm dissolved in 2012.
Couillard and Porter, both physicians, were previously appointed by Prime Minister Stephen Harper to the watchdog that monitors Canada's spy agency. Porter served as chair of the Security Intelligence Review Committee.
In the transcript, Porter is also quoted as saying assertions by Couillard that he "fooled" him were likely taken out of context and that he thinks the two men continue to have a "healthy relationship."
"I would say the relationship was close," Porter said about Couillard, a former health minister.
"We spoke about more than work, things we were going through. And many personal things I won't go into here, because they are personal. In the posts we held, one does not have many friends."
Later on Wednesday, a frustrated Couillard told a Cogeco radio station he didn't want to comment about Porter's jailhouse disclosure.
"This question, for two years, I've been asked about it every day," he told Quebec City's FM 93 in an interview.
"I won't say I'm fed up, but almost. I've admitted that I had a friendship with him. That's not the question. The question is: does the fact that I knew him allow people to associate me with what he's accused of?"
The transcript was posted on a new website titled, "Arthur Porter: Illegal in La Joya," which Todd said was set up by Porter's children.
Todd said in an interview Wednesday it was Porter's decision to speak out about his relationship with Couillard amid widespread media interest churned up by the election campaign.
"Obviously, as the election is getting closer, Arthur felt he had something to say," Todd told The Canadian Press from Ottawa.
"Clearly, if he wanted to have his opinion heard, now would be an ideal time to say it, wouldn't it?"
The biographer said he believes Porter had been thinking about talking publicly about Couillard for some time, even before the start of the campaign.
Todd was asked if he thought the endorsement was a deliberate attempt by Porter to hurt Couillard.
"I don't think so," said the author of Porter's biography, which is set for release in September.
"I honestly don't think it's my place to say one way or the other. I think it will mean different things to different people."
But Todd confirmed he had received a query last month about Couillard from a PQ strategist, who reached out to him on Twitter.
Todd said he ignored Yves Chartrand's request for details about Couillard that will be in his upcoming book.
He said he doesn't believe Porter has been in touch with the PQ, either, though he noted the Sierra Leone-born doctor was aware of the political request.
Porter was arrested last year in Panama and faces numerous charges in Quebec in connection with the awarding of the $1.3-billion hospital contract — one of Canada's biggest infrastructure projects.
He faces charges of fraud, conspiracy to commit fraud, fraud against the government, breach of trust, money-laundering, and accepting bribes. His wife Pamela, who was also arrested, faces charges of money-laundering and conspiracy.
Porter claims he's done nothing wrong.
Last week, Couillard was grilled extensively during the leaders' debate about his ties to Porter and he took issue with being mentioned in the same breath as the ex-hospital boss.
"He's someone I knew but to associate me in any way whatsoever with what he's accused of doing is unacceptable — unacceptable," Couillard said.
"I wasn't even around him when the contract was handed out."
On Wednesday, Marois was asked on the campaign trail about Porter's comments.
"I will tell you something that my mother used to tell me, 'Birds of a feather, flock together,'" Marois said.
"I think that Mr. Couillard has always tried to dissociate himself from Mr. Porter. We have always had some doubts. We understand that today Mr. Couillard's friend wants to give him a hand."
Coalition Leader Francois Legault also fired a shot at Couillard over Porter's remarks.
"With friends like that, who needs enemies?" Legault told reporters.
Porter also explained in the transcript why he and Couillard decided to go into business together.
"We were both finishing one career and looking for the next," said Porter, who noted the company was to be called "Porter Couillard."
"I had completed what I wanted to do at (the McGill University Health Centre), and he had to decide if he wanted to continue in the political arena or would go into commercial business...
"We never activated the company, pending the fact I was still basically at the MUHC and we wanted to wait until those strings were cut."
Porter was also asked whether he still considers Couillard a friend.
"Yes. I do not believe in 'fair-weather' friendship."
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