Comeau, who is one of 10 Nova Scotia senators, said his decision to retire early is not related to the expense scandal that has consumed the Senate for the past six months.
"It has nothing to do with the scandal, no. You can trust me on that," Comeau told reporters on Wednesday.
"I'm not leaving with any clouds over my head. I'm as clean as a whistle."
The 67-year-old senator, who is from Meteghan Station, became a senator in 1990 on Brian Mulroney's recommendation. Before that, he served as the Member of Parliament for West Nova for four years between 1984 and 1988.
Comeau said he actually decided two years ago that he would retire, and informed Prime Minister Stephen Harper in June that he'd be leaving.
Then Comeau was asked to chair the committee at the centre of the Senate scandal — Internal Economy, Budgets and Administration — which handled the review of Senator Pamela Wallin this summer.
"Marjory LeBreton asked me if I would take on this last assignment because the previous Internal Economy chair had to undergo some medical treatment, so I did accept to take on the role of chair of the Internal Economy committee until the fall," said Comeau.
"I asked if my resignation, my retirement could be kept kind of low key in order not to become a lame duck because the last thing you want is to spend a number of months, everybody knowing that you're retiring."
Comeau said a "very capable" person had been tapped to take over as chair of the committee, but refused to divulge any details.
His retirement is effective next Thursday.
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