Egyptian Ibrahim Suleiman in October rammed his truck into a vehicle carrying three US soldiers, in what the US embassy described as a "terrorist attack".
The soldiers were unharmed but the driver was lightly wounded when his truck caught fire as a result of the collision.
Kuwaiti authorities said at the time that police found a handwritten note on Suleiman in which he pledged allegiance to IS. They also said that he was carrying suspected explosives.
The supreme court today also upheld a 20-year jail term against Fahad Farraj, reportedly the de facto head of IS in Kuwait and the ringleader of an eight-member convicted IS cell.
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The court also upheld 15- and 10-year jail terms for the other seven members of the cell, five of whom are Kuwaiti citizens. The remaining three do not hold any citizenship.
The eight were convicted of fighting with IS in Syria and Iraq and of raising funds for the group.
Kuwaiti courts have given hefty jail terms to dozens of men charged with joining or sympathising with IS.