Founded, which already operates in the same building as Iris, will join the company's network, which now spans 15 offices worldwide and 1,000 staff.
Iris made the acquisition to build out its B2B offering for brands across business marketing, creative technology and strategic planning.
Founded’s San Francisco office, which opened in 2015, also offers the company a foothold in the US market.
Since Richard Mabbott and Richard Perry created the agency, Founded's 50-strong team has been behind various in-store stunts including PayPoint's first campaign in 2014.
Its roster of clients now includes Yazoo, Sony and Uniqlo.
Last year, Iris won Event's Best Digital Experience award for its #NEOrunway campaign with Adidas NEO.
Ian Millner, Iris CEO, said: "I’ve known Richard and Richard for a long time… the business they are building at Founded speaks for itself. I know that they will continue to flourish as part of the Iris network and equally, as part of our extended Cheil ‘Network Built For Now’ idea."
Richard Perry, partner at Founded, added: "We have only one priority – to serve our clients with the very best skills and resources we have access to – we’ve now strengthened our ability to do this. We’ve both watched and admired Iris for many years and love and respect what they do.
"We’re a young and ambitious agency and we know that being part of a great family like Iris will help accelerate both our creative and growth ambitions."
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