Major Nidal Hasan has been found guilty of killing 13 people and wounding more than 30 others at the Fort Hood military base.
The army psychiatrist could face the death penalty after military jurors reached unanimous verdicts on all 45 counts of premeditated murder and attempted murder.
Hasan gave no visible reaction as the verdict was read out.
The jury will begin hearing the "penalty phase" of the court martial on Monday and make a recommendation to the judge, who will determine the sentence.
If the death penalty is approved, Hasan would face death by lethal injection for the 2009 shooting spree on the Texas base.
The 42-year-old defended himself during the 13-day trial but chose not to call witnesses or testify and questioned only three of prosecutors' nearly 90 witnesses.
In statements to the judge the American-born Muslim suggested that he believed the attack was justified as a jihad against the US military campaigns in Afghanistan and Iraq.
Hasan never denied opening fire in a crowded waiting room at Fort Hood, where unarmed troops were making final preparations to deploy to Afghanistan and Iraq.
All but one of the dead were soldiers, including a pregnant private who curled on the floor and pleaded for her baby's life.
The sentencing phase is expected to begin with more testimony from survivors of the attack in a medical center where soldiers were waiting in long lines for immunizations and medical clearance.
About 50 soldiers and civilians testified of hearing someone scream "Allahu akbar!" - Arabic for "God is great!" - and seeing a man in Army camouflage open fire.
Many identified Hasan as the shooter and recalled his handgun's red and green laser sights piercing a room made dark with gun smoke.
The military's death row has just five other prisoners and no other soldier has been executed since 1961.