Major Nidal Hasan has been convicted of premeditated murder for the 2009 shooting rampage at Fort Hood, Texas.
That means he is now eligible for the death penalty.
Military jurors found the army psychiatrist guilty over the attack that killed 13 people and injured more than 30 others at the military base.
The trial now enters a penalty phase, where prosecutors will ask jurors to sentence Hasan to death. Hasan is acting as his own attorney. But he did not call witnesses or testify, and he questioned only three of prosecutors' nearly 90 witnesses.
Through media leaks and statements to the judge, the American-born Muslim signalled that he believed the attack was justified as a way to protect Islamic and Taliban leaders from US forces in Afghanistan and Iraq.
Hasan acknowledged carrying out the attack in a crowded waiting room where unarmed troops were making final preparations to deploy to Afghanistan and Iraq. Because Hasan never denied his actions, the court-martial was always less about a conviction than it was about ensuring he received the death penalty.
From the beginning of the case, the federal government has sought to execute Hasan, believing that any sentence short of a lethal injection would deprive the military and the families of the dead of the justice they have sought for nearly four years.
Hasan, a Virginia-born Muslim, said the attack was a jihad against US wars in Iraq and Afghanistan. He bristled when the trial judge, Colonel Tara Osborn, suggested the shooting rampage could have been avoided were it not for a spontaneous flash of anger.
All but one of the dead were soldiers, including a pregnant private who curled on the floor and pleaded for her baby's life.
Prosecutors never charged Hasan as a terrorist - an omission that still galls family members of the slain and survivors, some of whom have sued the U.S. government over missing the warning signs of Hasan's views before the attack.