Nidal Hasan, who said he wanted to be a martyr, faces death by lethal injection for the rampage at Fort Hood, Texas, which also wounded 31 people, but his execution will require presidential approval.
Hasan was sentenced to death on Wednesday by a military jury at Ford Hood. He had opened fire with a laser-sighted handgun at the sprawling central Texas military base just weeks before he was to be deployed to Afghanistan.
Bearded and in a wheelchair after being shot by police trying to end the rampage, Hasan showed no visible expression as the president of the jury read aloud the sentence.
Death sentences are rare in the military which last executed a member of the service 52 years ago. Hasan, 42, insisted on representing himself but gave no evidence in his defence.
He would have to be executed in a civilian jail as no military prison has a death chamber.