Prosecutors had previously demanded the court should sentence Arman, alias Galaxi bin Abdul Somad, to 20 years for his role in the bombing in the eastern city of Makassar, capital of South Sulawesi province, 1400 km east of Jakarta.
The panel of judges agreed with the prosecution that Arman transported and hid the lethal device before passing it on to the actual bombers in advance of the December 2002 blast.
They also said the defendant helped survey the scene beforehand.
"We declare the defendant guilty of taking part in an evil conspiracy and helping a terror crime," said presiding judge Jasolo Situmorang in his verdict at the Makassar district court.
Arman responded with a smile. The maximum penalty for such a crime is death.
The verdict brought the number of people convicted over the case to 16, with sentences ranging from two to 18 years.
Hunt for mastermind
Police are still hunting for the mastermind of the bombing. It was one of a number of deadly bomb attacks in the world's most populous Muslim nation in the past two years.
The worst, in Bali last year, killed 202, most of them foreign tourists.
Authorities had said there was evidence linking the Makassar blast to the Bali bombings as some of the suspects knew those on trial over the attacks on the resort island.