The RCMP won't press criminal charges against Independent Senator Pamela Wallin for irregularities in her Senate expenses.

"The RCMP has completed its thorough investigation into Senator Pamela Wallin's Senate expenses," assistant commissioner Gilles Michaud said in a statement Thursday. "Following consultation with Crown counsel, the RCMP has determined that no criminal charges will be laid against Senator Wallin and will be concluding its investigational file."

Wallin said Thursday she was happy to have avoided further scrutiny.

"I am relieved that the nightmare is over," Wallin told CBC News as she hurried out of a taxi and into Parliament Hill's Centre Block Thursday afternoon.

Senator Pamela Wallin responds to news that the RCMP is dropping it's investigation into allegations of fraud and will not be laying charges. 0:37

The move comes less than a month after Senator Mike Duffy was cleared of all 31 criminal charges he faced relating to his living expenses, travel claims and service contracts. The Crown has also dropped all criminal charges against retired senator Mac Harb for similar alleged offences. Senator Patrick Brazeau has been charged and is still awaiting trial.

'Excruciating' ordeal

The senator's lawyer, Terrence O'Sullivan, said it was a tremendous relief for Wallin to be cleared after a nearly three year-long investigation. "This has been an excruciating three years for her and for her family. It has had an enormous personal toll on her," he said in an interview with CBC News, noting both her parents died before she could be cleared of criminal wrongdoing. "It was unwarranted, it was unnecessary."

O'Sullivan said that Wallin was never given the opportunity to defend herself, or her actions, to the Senate's internal economy committee, which ultimately made the decision to forward her file to the RCMP for review.

An independent audit by Deloitte published in May 2013 recommended she pay back some of her travel expenses but they found no instance of criminality, he said. She was also not given the opportunity to have her file reviewed by former Supreme Court Justice Ian Binnie who presided over a binding arbitration process with other senators who were fingered by the Auditor General for questionable or ineligible expenses. "The hallmarks of fairness were not afforded to Senator Wallin," O'Sullivan said.

"We have to sit down and consider what we're going to do going forward, if anything, and that decision has yet to be made," he said, when asked if she would seek some sort of compensation for the ordeal.

"I don't think she has been treated fairly in any way shape or form by the Senate," he said, adding she is considering making a request for pay denied to her during her nearly two-and-a-half year suspension.

The Mounties had been reviewing 150 Senate expense claims made by the former broadcaster and diplomat, including those for 24 trips related to her work on corporate boards, according to documents filed in court in March 2015.

Investigators initially said they believed Wallin had filed expense claims twice — once with the Senate and once with those companies — and that the move was tantamount to committing fraud and breach of trust.

The Mounties had also alleged she billed the Senate for trips between her home in Saskatchewan and Toronto that were unrelated to parliamentary business.

"I believe that Senator Wallin's conduct represent[s] a serious and marked departure from the standards expected of a Canadian senator," Cpl. Rudy Exantus said in an affidavit filed in court.

The expense claims were filed between Jan. 15, 2009, shortly after Wallin was named to the Senate, and Sept. 25, 2012.

Wallin has long maintained that her office may have made errors in filing expense claims. She has since apologized and paid back $154,191.29.

'Good for Senator Wallin'

Wallin, along with Duffy and Brazeau, was suspended without pay from the Senate at the height of the expenses scandal in November 2013. It was the first time in the Red Chamber's history that a senator had been sanctioned in that way over expenses without being convicted of a criminal offence.

Conservative senators — her former caucus colleagues — voted largely in favour of the suspension whereas the Senate Liberal caucus voted against it, arguing the move deprived them of their right to due process.

"I think it's an extremely sad day for democracy. If we can't expect the rule of law in Canada, then where on earth can we expect it?" Wallin said at the time.

Wallin's suspension ended when former prime minister Stephen Harper called an election last August. She has been sitting in the chamber since the return of Parliament last fall.

Senate Liberal Leader Jim Cowan reiterated Thursday that he was opposed to Wallin's suspension because she was not facing criminal charges.

"Good for Senator Wallin," Cowan said outside the Senate chamber. "I'm sure that's a great relief to her. She's had that hang over her head now for a couple of years," he said.

"I was opposed to the way that the Senate dealt with the senators at the time. The government of the day ... rammed through the suspension motions. Senator Wallin and several other senators were deprived not only of the right to sit in the senate but of their pay for an extended period of time," the senator said, noting it will be up to those formerly suspended senators to make the case for back pay.

"The cloud is gone, she can get on with her life," Senate Liberal Jim Munson added.

"I've always said, in terms of that suspension, this was a political game from the get-go. There were a number of senators who didn't want her in here [in the chamber]. I've always been a due process person, I've always said they weren't treated fairly."

Conservative Senator Don Plett, one of few Tories who abstained on the suspension vote, said Thursday he was "very happy" about the RCMP's decision. "That closes another chapter of the Senate's life," he said.

Speaker of the Senate George Furey said in a statement Thursday that he "respects the decision of the RCMP.

"Given that the investigation is now completed, the matter is considered closed."