A total of 29 defendants, seven of them women, had been on trial on charges of helping a Saudi suicide bomber carry out the June 26 attack, which killed 26 Shiite worshippers, including 2 Indians, and wounded 227.
Among those sentenced to death were one defendant convicted of driving the bomber to the mosque and a second described by the court as the "wali" or leader of the local branch of IS. Both were in court.
The court acquitted 14 defendants and sentenced the rest to jail terms of up to 15 years.
The defendants included seven Kuwaitis, five Saudis, three Pakistanis and 13 stateless Arabs known as bidoon, as well as one unidentified person still at large.
An IS-affiliated group calling itself Najd Province claimed the Kuwait City bombing as well as suicide attacks at two Shiite mosques in Saudi Arabia in May.
The Sunni extremists of IS consider Shiites to be heretics and have repeatedly attacked Shiite targets around the region.