Opposition parties trained their sights squarely on Mr Sajjan, who apologised again in the House of Commons.
The Operation Medusa was one of the bloodiest and most pivotal battles of the Afghan war.
Interim Conservative leader Rona Ambrose called it a "cardinal sin" in the military circles for stealing valours of others.
"How much more does the Prime Minister need to hear before he understands why our men and women in uniform have lost confidence in the Minister," Ms Ambrose said.
Mr Trudeau, however, would not be moved from his talking points.
"The Minister made a mistake," the Prime Minister said repeatedly. "He acknowledged his responsibility and apologised for it; that's what Canadians expect when one makes a mistake," The Toronto Sun reported.
Mr Trudeau went on to insist that Mr Sajjan had served his country with distinction in a number of capacities, including as a police officer and as a soldier. As a Minister, he added, "He has my full confidence."
However, his apology did little to assuage the opposition, with both the Conservatives and the Democratics calling on Mr Trudeau to sack him.
"It's not an error when you keep repeating the same lie," New Democratic Party Leader Tom Mulcair said after question period.
In speech in New Delhi on April 18, Mr Sajjan told a think tank that he had been the "architect" of Operation Medusa, which the Minister has since retracted.
"On my first deployment to Kandahar in 2006, I was kind of thrown in an unforeseen situation and became the architect of an operation... where we removed about 1,500 Taliban fighters," Mr Sajjan said in his speech.
The Canadian Defence Minister was a Major with the Canadian Forces in Afghanistan during Operation Medusa, and received a special commendation.
Hundreds of Taliban terrorists were killed or captured over a two-week period. Twelve Canadians were also killed in the fighting.
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