Maarik al Tawaiha was found guilty of killing three US trainers and sentenced to "hard labour for life," a term that usually lasts 20 years but could stretch to a full lifetime.
A Jordanian court on Monday sentenced a soldier to life imprisonment over the killing of three American military trainers outside an army base last year.
The military court in Amman found 39-year-old Maarik al Tawaiha guilty of shooting the trainers as they waited to enter the King Faisal base at Al Jafr in southern Jordan on November 4.
The charge sheet did not indicate that he had any ties to militant groups.
The court sentenced him to "hard labour for life," a term that usually lasts 20 years but could stretch to a full lifetime, a judicial official said.
It also demoted him from sergeant to second private and threw him out of military service.
The prosecution in June accused him of "voluntary manslaughter" as well as "insulting the dignity and reputation of the armed forces and violating military orders."
Tawaiha, who wore a suit at the hearing, had been in custody since November but denied the charges.
The court had heard evidence from base guards and forensic experts.
Exchange of fire
The Jordanian army said in November that the shooting took place during an exchange of fire at the gate of the base after the car carrying the US trainers failed to stop.
An American defence official described the incident as "green on blue," a military term for when friendly forces attack US personnel.
Tawaiha told the court he had opened fire on the cars carrying the American trainers after hearing gunshots. Suspecting an attack on the base, he shot at them, killing the three Americans and wounding a Jordanian soldier.
The American official said that it was not clear whether the act was a deliberate attempt to kill US personnel or "some kind of misunderstanding."
The King Faisal air base hosts trainers of various nationalities, including Americans.
Jordan, which hosts some 2,200 American military personnel, is a key American ally and a member of the United States-led coalition fighting Daesh.
US forces have trained a small group of vetted Syrian rebels in the country, and American instructors have also trained Palestinian security forces there over the past few years.
Tens of thousands of Iraqi, Yemeni and Libyan forces have also received training in Jordan.
In 2015, the United States said it would increase overall US assistance to Jordan from $660 million to $1 billion annually for the period to 2017.
The Al Jafr incident came almost a year after a Jordanian policeman shot dead two US instructors, a South African and two Jordanians at a police training centre east of Amman, before being gunned down.