Senator Mike Duffy is suing the federal government for nearly $8-million, saying the Senate and the RCMP unjustly made him a scapegoat in the politically damaging Senate spending scandal.

Mr. Duffy argues in his statement of claim that he was punished in the court of public opinion during the four-year ordeal, and continues to suffer physical, emotional and financial hardship. He said his acquittal on 31 criminal charges at trial last year showed that fellow members of the Senate and the national police force treated him unfairly.

Mr. Duffy alleges the Senate and a majority of senators "acted unconstitutionally" when he was suspended without pay in 2013, and that the RCMP singled him out in its investigation because he was a "more high-profile target" than Nigel Wright, a former Conservative official who gave him $90,000 to repay expense claims that had become controversial.

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Mr. Duffy's lawyer, Lawrence Greenspon, announced the suit, which was filed in Ontario Superior Court, at a news conference in Ottawa on Thursday afternoon.

"We have somebody who's been through the public grinder," Mr. Greenspon said of his 71-year-old client. "I would think that the public would be and should be sympathetic to somebody who was put through what Mike Duffy was put through at the behest of, for the most part, people who are supposed to be our political representatives."

Mr. Greenspon said the civil suit, which comes almost a year and a half after the end of the criminal trial, was initiated after a "considerable amount of thought."

"It's been extremely difficult for Senator Duffy, his wife and his kids. And there was an understandable reluctance to get back into the public eye," he said.

In a statement, Mr. Duffy said he hopes his legal action will eventually lead to removal of some of the powers Parliament has over its employees.

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"My family and I have suffered stress and serious financial damage, as have the other Senators who were unfairly targeted, and their rights trampled," he said. "If this action succeeds in bringing Charter protections to all who work on Parliament Hill, this will be my greatest contribution to public life."

Former prime minister Stephen Harper appointed Mr. Duffy, a former television journalist, as a Conservative senator in 2009. He now sits as an Independent. In 2013, the Senate was engulfed in controversy over the living allowances and expense claims of Mr. Duffy and senators Pamela Wallin and Patrick Brazeau. The Senate suspended all three.

Mr. Duffy was charged in July, 2014 with fraud, breach of trust and bribery in relation to his Senate expense claims and consulting contracts, and for accepting the $90,000 payment from Mr. Wright, then the chief of staff to Mr. Harper. In April, 2016, Ontario Court Justice Charles Vaillancourt said the Senate rules on expense claims were unclear, and acquitted Mr. Duffy on all charges.

The statement of claim said the ordeal caused Mr. Duffy "pain, suffering and loss of enjoyment of life." It cited lost friendships, "extreme damage" to his reputation and lost job opportunities, as well as mental and physical distress, including severe anxiety, depression, nightmares and aggravation to his heart condition.

"Senator Duffy's acquittal at trial has not remedied his damages," the statement said. "A significant stigma still remains. Senator Duffy continues to suffer emotional and physical damage due to the continued and prolonged reputational damage that continues to this day, including daily mention, mockery and ridicule in media outlets nation-wide."

At the heart of the lawsuit is the fact that Mr. Wright was never charged in connection with the $90,000 payment, and instead testified against Mr. Duffy at the trial.

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"The RCMP believed that charges against Nigel Wright would weaken the case against Senator Duffy, whom they made the prime focus of the investigation," the statement of claim said. "The RCMP further believed that although Mr. Wright was influential and held an important position, Senator Duffy was a more high-profile target."

The statement of claim alleges that this "produced an investigation blinded by tunnel vision and incorrectly focused on Senator Duffy, excluding other potential actors on the basis of their value, to the detriment of Senator Duffy and to the detriment of the Canadian public as a whole."

In a statement, RCMP spokeswoman Annie Delisle would not comment on the case because the matter will be before the courts.

Sébastien Grammond, a professor of law at the University of Ottawa, said it will be a challenge for Mr. Duffy to persuade the court he deserves compensation for being investigated and charged by the RCMP. Prof. Grammond said there is clear jurisprudence involving compensation to people who were wrongfully convicted, but he said "it's an entirely different matter when it comes to someone who was charged and acquitted.

"The bar will be high," he said, pointing out that Mr. Duffy's lawyer will have to prove that the RCMP acted with malice.

In relation to his suspension from the Senate, Mr. Duffy alleged in his statement of claim that he was "punished in the absence of procedural fairness, and then only for purely political motives." Mr. Duffy's lawsuit also argues that his expenses were appropriate and that he was forced to agree publicly to pay back the amount as part of a damage-control exercise, even though Mr. Wright was actually picking up the tab.

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"After being threatened, cajoled, arm-twisted and rebuked, Senator Duffy capitulated," the statement of claim said. "He was extorted into agreeing to release a statement that he had claimed amounts in error and that he would pay the amounts back, a statement that would deceive the Canadian public and the Tory base."

Mr. Greenspon also took issue with the Senate for docking $17,000 in expenses, which were among those discussed at his trial, from Mr. Duffy's pay when he returned to the Red Chamber after his acquittal. However, he argued the civil lawsuit should not lead to a re-examination of Mr. Duffy's expense claims.

The Senate's interim law clerk, Jacqueline Kuehl, said in a statement: "As this is a matter before the courts, we will respect the process and will not be commenting until such a time as is appropriate to do so."

Mr. Duffy is suing the Senate and the Attorney-General of Canada for $6.5-million in general damages, $300,000 for loss of income and benefits and $1-million in punitive damages. When asked if he is working pro bono, Mr. Greenspon laughed and said, "Mike Duffy is not a rich man. That's all I'm going to say on my retainer."