Kearon, a former marketer at Unilever's Elida Gibbs division, set up Brainjuicer in 2000. The agency has done consumer research for big-name clients including Adidas, Kellogg and McDonald's.
Brainjuicer trumped other consumer brands, such as Green & Blacks chocolate and Friends Reunited, to win the London prize.
Kearon said: "It was great to see market research companies gaining recognition for innovation."
BrainJuicer was not the only market research firm to be honoured. Charlie Osmond and Caroline Plumb, co-founders of market research agency Freshminds, were also jointly nominated for the young entrepreneur of the year award.
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