The Somewhere Only We Know hitmakers have racked up four number one albums and more than 13 million sales worldwide.
Keane last appeared as part of Forest Live in 2010 but will be back in 2021.
They will be playing at Westonbirt on June 11.
Forest Live is an outdoor music series that introduces forests to new audiences in unique, natural woodland arenas around the country.
More than 1.9 million people have attended a Forest Live gig in the last 20 years.
Tickets are on sale from tomorrow at 9am. Visit www.forestryengland.uk/music