OTTAWA -- Longtime Sen. Colin Kenny is calling it quits months before his scheduled retirement later this year.

Kenny officially notified the Governor General on Wednesday morning that he will leave the Senate at the end of the week, ahead of his mandatory retirement date in December.

In a short letter to Rideau Hall, Kenny cites his health and his decades in the upper chamber as his reasons to leave at the end of business on Friday.

"I have been experiencing continued ill health and feel the time has come to retire," the resignation letter says.

"I think I have done my bit.

"It has been my great privilege to serve my country over the last forty-four years, both in the office of Prime Minister (Pierre) Trudeau and as a member of the Senate."

The elder Trudeau appointed Kenny to the Senate in the spring of 1984 after he spent a decade as a special adviser and assistant principal secretary in the Prime Minister's Office.

The ensuring 34 years saw Kenny focus on military and security issues, becoming an outspoken critic of cuts to defence spending.

But his tenure was marked by testy exchanges when he headed the Senate's defence committee, the most memorable of which live online in videos capturing political bickering between Kenny and fellow senators.

More recently, questions were raised about his conduct in relation to the workers in his office. In 2014, a Senate-appointed investigator cleared Kenny on allegations of sexually and verbally harassing his office staff.

Two years ago, Kenny repaid more than $30,000 in expenses that were deemed unjustified after they were flagged in an auditor general's report on Senate spending.

Kenny is not the only senator who has opted to leave the upper chamber before hitting the mandatory retirement age of 75.

Claudette Tardif, a Liberal from Alberta, announced last week that she would officially retire from the Senate on Friday. Fellow Liberal Joan Fraser will also retire on the same day, one year before her mandatory retirement date.

Four more senators are scheduled to retire by the end of the year. There are already 11 seats vacant in the upper chamber.