Pentagon prosecutors allege that Khadr, then 15, planted land mines for al-Qaeda and threw a grenade in a firefight with U.S. troops in Afghanistan that fatally wounded a Special Forces medic, Army Sgt. First Class Christopher Speer.
He faces a maximum of life in prison if convicted.
But Khadr told his military judge, Army Col. Patrick Parrish, that he had spurned U.S. government offers of a secret plea deal that would have him admit to war crimes in exchange for a 30-year sentence, of which he would serve only five.
Khadr said he rebuffed the deal because pleading guilty would "give an excuse to the government for torturing me and abusing me as a child."
His family attorney, Dennis Edney, later said that the offer, made about a month ago, was for release from detention at Guantanamo in 2015 - and continuation of the sentence in his native Canada.
"Mr. Khadr could not admit to guilt to something he did not do," Edney said.
War-court officials refuse to discuss plea agreements before they are complete.
Khadr threw his Aug. 10 trial date into uncertainty last week by firing his defense attorneys. In rapid succession Monday, he confirmed that he voluntarily fired his team, said that his trial was meant to appease American public opinion, and confirmed a plea deal that had been the source of Canadian media speculation for months.
Left unclear is what would become of a still-incomplete motion to exclude from his trial his 2002 and 2003 confessions during military interrogations as the fruit of torture and coercion.
Two months ago, his defense team had called ex-intelligence forces to describe the teen's black-hooded, shackled treatment and stretcher-bound interrogations in Afghanistan. Doctors had saved him and his eyesight from bullet and shrapnel wounds.
The military judge Monday instructed Khadr's Pentagon-appointed counsel, Army Lt. Col. Jon Jackson, to defend him over the captive's objections, saying, "I want to make sure the proceedings are fair to Mr. Khadr - whether he boycotts or not."