Perrin testified that Ray Novak, Harper's current chief of staff, was in the same room as Harper's former chief of staff when Wright made it known he would use his own funds to repay Duffy's ineligible senate expenses in March 2013.
Duffy has pleaded not guilty to 31 charges of fraud, breach of trust and bribery related to expenses he claimed in 2013 as a senator and later repaid with money from Wright.
Harper has maintained he was not told of Wright's decision to personally repay Duffy's expenses, and repeatedly said the two individuals responsible — Duffy and Wright — are being held accountable.
Perrin, 36, is an accomplished lawyer and a life-long Conservative. In 2013, he served as Harper's legal counsel. His job was to stay at arm's length, enough to offer a dissenting opinion.
Veteran journalist Dan Léger, who has authored Duffy: Stardom to Senate to Scandal, a book about Duffy's rise and fall, has been keeping a close eye on the Senate expenses scandal and the senator's criminal trial.
"If Perrin is calling it like he sees it, then fair enough, that's what the courts are for," Léger said in an interview with CBC News.
Perrin, whose Conservative roots run deep, was 22 years old when the Canadian Alliance picked Harper as its new leader in 2002.
"I think we can move forward with Stephen Harper as leader and I'm confident in his policies and the direction we'll be heading in," a young Perrin said.
Harper merged the Alliance with the Progressive Conservatives, and in 2006 Harper's Conservatives were elected to government.
Honoured by U.S.
Perrin went to law school earning a Master of Laws (with honours) from McGill University in 2007. He is also an internationally recognized authority on human trafficking. He was honoured for his work by the U.S. State Department in 2009 while pushing for tougher laws in Canada.
"We're calling on a federal action plan that works to prosecute human traffickers more effectively," Perrin said at the time.
In 2012, when the Harper government was reworking Canada's prostitution laws, his advocacy and party ties brought Perrin back into the Prime Minister's Office.
Working under Wright, he didn't have a direct line into the prime minister, but on issues such as Duffy's Senate expenses, Perrin spoke his mind.
'Difference of opinion'
"Let's just say that there was a difference of opinion, and that Perrin was evidently one of the very few people who was willing to express that," Léger said.
Perrin did a legal review of the agreement Wright struck with Duffy. But after the cheque was signed, Perrin abruptly left the PMO citing family issues.
He has since returned to the University of British Columbia where he works as an associate professor at the Peter A. Allard School of Law.
Perrin's testimony in court was consistent with the deposition he gave to the RCMP before they laid charges against Duffy.
"He doesn't depend anymore on Stephen Harper for his livelihood," Léger said.
Also on HuffPost