Ali Imron admitted helping plot the attacks, which police blamed on the al-Qaida linked Jamaah Islamiyah (JI) network, as well as assisting in the construction of the van-bomb detonated in the heart of Bali's tourist strip.
A total of 202 people, mostly western tourists, were killed when separate bombs exploded almost simultaneously near a bar and nightclub on 12 October 2002.
"We sentence the defendant...to the punishment of jail for life," said chief judge Lilik Mulyadi. Imron, 33, appeared calm when the sentence was read out but appeared to be frowning when two policemen later led him away.
The sentence was heavier than the 20-year jail sentence sought by prosecutors, but less than the maximum penalty of death which can be imposed in such cases. Two other members of the Bali bomb plot, including Imron's brother Amrozi, have already been sentenced to death.
Mulyadi said Imron had committed "an extraordinary crime and a crime against humanity."
However, the judge said Imron "had felt guilt and has honestly expressed regrets." He was polite throughout the trial and had realised that the blast "was a mistake according to Islam," the judge said.
The court had earlier found Imron guilty of planning an act of “terrorism”.
"I am guilty and I can only seek forgiveness from my family, my friends, the family of victims and the victims"
Bali bombing suspect
The judges said Imron had admitted helping to build the bomb and drove it to an intersection close to the Sari nightclub. Another driver then detonated it outside the nightclub after the suicide bombing inside the nearby Paddy's Bar.
Judges also said Imron admitted to planting a bomb near the US consulate in Denpasar. The bomb, detonated by remote control, caused minor damage and no casualties.
They said he attended several planning meetings, surveyed the targets, helped transport bomb-making chemicals to the island. He also helped a fugitive Malaysian called Dr Azahari - allegedly a top JI bombmaker - to build the Sari Club bomb.
Judges said the defendant had admitted teaching a suicide bomber how to detonate an explosives-stuffed vest and showed another man, Arnasan, how to activate a remote detonator for the van bomb.
The suicide bomber, Feri alias Isa, wore the vest into Paddy's Bar across the road from Sari Club.
Imron is the only Bali bombing accused to publicly express remorse. "I am guilty and I can only seek forgiveness from my family, my friends, the family of victims and the victims," Imron told the trial.
Statements like that, along with what prosecutors called his straightforward testimony, prompted prosecutors to call for a 20-year sentence rather than death.