Judge Nyoman Gede Wirya, presiding over the state court in Denpasar, the Balinese capital, said Abdul Aziz, 30, was guilty of the primary charges of "engaging or taking part in" an act of terrorism.
Aziz was found guilty of creating a website for Azahari Husin and Noordin Top, senior members of Jemaah Islamiyah (JI)who were both alleged to have masterminded the Bali attack. Husin was killed in a police raid in 2005.
Aziz was also convicted of harbouring Noordin, one of Asia's most wanted men who has eluded capture by Indonesian police several times and remains on the run.
Judge Wirya said Aziz - who also set up a website calling on Muslims to wage war against "infidels" - committed "a gross crime against humanity" through his actions.
Aziz's lawyer said he may appeal against the sentence.
The suicide blasts, which singled out three restaurants on the island popular with tourists last October, also wounded more than 150 people.
Three other suspects accused in the 2005 bombings are charged with harbouring Noordin or making or transporting the explosives used in the attacks.
Their verdicts are expected in the next few days.
The Jemaah Islamiyah group has also been blamed for the 2002 Bali bombings in which 202 people, mainly tourists from Australia, were killed when two bombs exploded in the busy nightclub area of the island.
In June this year, the Indonesian authorities released Abu Bakr Bashir, a Muslim religious leader alleged to have founded the group, after serving two years in prison for conspiracy over the 2002 bomb plot.
The decision caused widespread anger among victims' families and the Australian government, which said his sentence had been too lenient.