The agency, forged during a "Champagne-fuelled" conversation at an awards dinner last year, will launch having worked on briefs for Thomas Cook and with clients including Sarah Beeny’s online property site Tepilo.
Campbell said: "We like to do things a bit differently. After five years of Illuminate we are opening the doors to Campbell Brown with some great names already under our belts.
"Thomas Cook and Sarah Beeny are among clients we are proud to have already worked with and advised together so far, while we have been setting up the partnership behind the scenes."
Illuminate’s client roster includes Confused.com, Royal Institute of British Architects and decoration e-commerce site A Shade Wilder.
Brown, who was a senior account manager at Manifest London, added: "I'd been agency side for more than five years and was ready for something new, exciting and, to be honest, my own.
"I'm not one to shy away from hard work and getting my hands dirty, so taking the leap to go at it with a partner was a no-brainer - I am excited for the stress and sleepless nights."
At Manifest Brown worked on clients including Scottish drinks company BrewDog and fancy dress supplier Morphsuits.