"Ferrari announces that Scuderia Ferrari has renewed its technical and racing agreement with Kimi Raikkonen," a team statement read.
"The Finnish driver will therefore race for the Maranello team in the 2018 Formula One World Championship."
Raikkonen's signature comes after he chased home Sebastian Vettel in a dominant Ferrari display in the Hungarian Grand Prix last time out.
Vettel, who increased his lead over Mercedes' Lewis Hamilton to 14 points, has yet to confirm his plans for 2018.
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"I think I have been public on the Sebastian issue, if he wants to stay he is more than welcome to stay," said Ferrari president Sergio Marchionne after Hungary.
For Raikkonen, 37, Tuesday's deal secures his fifth consecutive season with Ferrari after an initial spell at Maranello when he captured the world title in 2007.
He is placed fifth in the 2017 drivers' standings on 116 points ahead of Sunday's Belgian Grand Prix at Spa- Francorchamps.