The court convicted the men of offences including carrying out terrorist acts resulting in death, possessing weapons and ammunition for terrorist purposes and promoting the ideology of a terrorist group.
Two others were given six years in prison, a lawyer for the victims' families was quoted as saying.
The ruling is subject to appeal and automatic review by the Court of Cassation, Petra said.
Gunmen opened fire during a funeral at a Greek Orthodox church in the village of Hamoud on October 23, in a rare attack on Jordan's Christian minority.
Authorities said 34 people were also wounded.
Security forces arrested the three men on October 26 after a shootout at an abandoned house in Karak.
All three were wounded while no security personnel were injured, according to the Public Security Directorate.
Jordan later that day launched air strikes on southern Syria against groups it linked to the church attack.
Syrian authorities said seven people, including three children and a woman, were killed.
Jordan later acknowledged that its air strikes had killed civilians in Syria and the two countries agreed to form a joint security committee to review the incident and its consequences.
with DPA
