The band will play Portugal's Optimus Alive festival in Lisbon, which will take place on July 12-15 next summer.
The announcement follows the news that the group will play 10 dates across the US in February 2012, as part of their upcoming world tour.
The string of shows will start with their Stateside dates in February and will continue through the festival season and into November next year.
They are expected to confirm a collection of UK tour dates in the coming weeks after revealing a number of European gigs.
The tour will be in support of their latest album The King of Limbs, which reached number three on the UK chart earlier this year.
Radiohead have promised fans that most of their European shows will be held at indoor venues.
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Watch the music video for Radiohead's 'Lotus Flower' below: