Strahl was not forced to resign, and indeed had been fully cleared by the federal ethics commissioner of claims involving an alleged conflict of interest, Harper told the House of Commons.
"Chuck Strahl is one of the most honourable and decent people I have ever worked with in the Parliament of Canada," the prime minister said as the Conservative benches erupted with applause.
"It is a shame that for the sake of his personal reputation he decided he is no longer willing to provide his services."
Strahl announced his resignation from the Security Intelligence Review Committee late Friday afternoon before Parliament resumed Monday after a six-week Christmas break.
While maintaining that he was in full compliance with all rules, Strahl said in his resignation letter that he did not "wish to be in the centre of the political fray" after leaving elected office.
"Nor do I want to be a distraction from the important work SIRC does every day in ensuring the security of Canadians."
Strahl had been under increasing pressure since registering last month to lobby on behalf of Northern Gateway Pipelines.
The review committee Strahl chaired provides civilian oversight for the Canadian Security Intelligence Service — the spy agency that was revealed last year to be spying on environmental and other activists opposed to new pipeline construction, including the proposed Northern Gateway project.
Harper was responding to a question from New Democrat House leader Nathan Cullen, who wanted to know why the Conservatives failed to recognize Strahl's "blatant conflict of interest."
Democracy Watch, an independent parliamentary advocacy organization, wrote a letter of complaint Monday to Mary Dawson, the conflict of interest and ethics commissioner, asking her to re-examine Strahl's lobbying activities.
"Democracy Watch's opinion is that Mr. Strahl's work with Enbridge while being chair of SIRC while CSIS is investigating opponents of Enbridge's proposed Northern Gateway pipeline causes conflicts of interest, it does not prevent them," said the letter.
It also raised questions about a legislated two-year cooling off period for former cabinet ministers, noting that Enbridge lobbied Strahl and his department when he was still in office.
"There is enough clear evidence for Ethics Commissioner Mary Dawson to launch an inquiry into Mr. Strahl's activities," Duff Conacher of Democracy Watch said in a release.
Strahl, who came to Ottawa from Chilliwack, B.C., as a Reform party MP in 1993, earned a reputation as a hard-working straight shooter who avoided the more bitterly partisan antics of the politics game.
So it is a particularly bitter twist of political fate that he should be linked in any way to his predecessor at SIRC, who also left the spy watchdog amid questionable business dealings.
Strahl was named SIRC chairman in June 2012, replacing Dr. Arthur Porter.
Porter, appointed by Harper to SIRC in 2008 and elevated to chairman in 2010, resigned in December 2011 following published reports of his business links to an international arms dealer.
Porter has since been charged with several offences related to alleged scams in the awarding of a $1.3-billion Montreal hospital contract. He is currently in a Panamanian prison while Canada works to have him extradited to Montreal to stand trial.
Note to readers: This is a corrected story. An earlier version mistakenly identified Nathan Cullen as NDP deputy leader.
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