Cake was awarded the work following a four-way competitive pitch.
The agency will deliver a series of launch events, alongside partner agency My Beautiful City, in spring next year.
Andrew Casher, head of experiential at Cake, said there is a lot of excitement about the win in the office. "Both River Island and Rihanna have reputations for breaking the mould within their respective industries, so the chance to promote this hotly-anticipated collaboration to the UK and the world is a brilliant brief for us."
Josie Roscop, head of marketing for River Island added: "Cake’s innovative approach to launching globally-famous brands, backed up by its solid experience in experiential activity, PR and social media made it the obvious choice for us.
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