By Agence France-Presse
Nur Muhammet Abdullah Al Faris was arrested last December on the outskirts of Jakarta and charged over his part in plotting the planned assaults.
Al Faris had planned to assassinate Jakarta's police chief and orchestrate a suicide bombing at a mosque used by members of the Muslim Shia minority, a court heard. Neither of the intended attacks went ahead.
"The defendant is declared to be convincingly guilty of committing an evil conspiracy and assisting terrorism offences," Judge Novry Tammy Oroh told a Jakarta court.
The court heard that Al Faris -- a member of China's mostly Muslim Uighur ethnic minority -- hatched the plots under the guidance of Bahrun Naim, a leading Indonesian militant fighting with the Islamic State group.
Naim has been linked to several botched attacks in his homeland, ranging from a plot to fire a rocket at Singapore to a suicide attack on a police station.
He instructed another militant, Arif Hidayatullah, to assist Al Faris in carrying out the attacks by finding him accommodation and teaching him to make bombs.
Hidayatullah, who was arrested on the same day as Al Faris, was also sentenced to six years' prison last month.
There has been an upsurge of violence and attempted attacks in the world's most populous Muslim-majority country over the past year due to the growing influence of IS.
Last month police shot dead a man carrying knives and suspected pipe bombs after he launched a daylight assault on officers in an attack later claimed by IS.
Two militants were also jailed that month over their roles in this year's IS-claimed suicide bombing and gun attack in Jakarta that left four civilians and four attackers dead.