Officials say he will also face six charges of attempted murder and six counts of assault in connection with the March 11 shooting spree.
Bales, an 11-year military veteran, is being held at a military prison at Fort Leavenworth, in the midwestern state of Kansas. He is alleged to have walked out of his southern Afghanistan military post under cover of darkness and gunned down nine children and eight adults.
Relatives of Afghans killed in the the shooting massacre said Friday they want Bales' trial held in Afghanistan.
The killings further strained already shaky U.S.-Afghan relations, following a series of missteps, including the inadvertent burning of Qurans at a U.S. military base near Kabul.
Bales' civilian lawyer, John Henry Browne, has said his client was likely suffering from combat stress and post-traumatic stress disorder.
Bales, who served three tours of duty in Iraq before being deployed to Afghanistan last December, suffered a traumatic brain injury in Iraq in 2010. A day before the massacre, he witnessed one of his fellow soldiers get his leg blown off.