The chief judge at the Denpasar district court said that Anif Solchanudin, a 24-year-old mobile telephone salesman, was "proven without doubt to have participated in acts of terrorism".
Solchanudin had admitted that he had been interested in becoming a suicide bomber, but denied any advance knowledge of the attacks.
The prosecution had accused him of receiving training to become a bomber.
Judge Daniel Palitin also told the court that the defendant was guilty of charges of possessing explosives. Solchanudin had been found with 29 bullets in his possession.
Prosecutors had sought a 10-year sentence.
Palitin said that Solchanudin's "crime is a crime against humanity" and his acts had caused particular suffering to the families of the 20 bystanders killed in the attacks on three busy restaurants on the palm-fringed island.
He also noted that Solchanudin had persisted with his wish to become a suicide bomber, even though death sentences were meted out to three Islamic militants involved in the 2002 bombings in Bali which left 202 people dead.
"This crime caused many victims and loss and the people of Bali are still suffering until now," the judge added.
Solchanudin is the fourth man to be sentenced over the attacks, which are thought to have been masterminded by Malaysian Islamic extremists Azahari Husin and Noordin Mohammad Top.
The other three received sentences ranging from eight to 18 years earlier this month.