Lonergan will work with 20:20 clients including Audi, BP Ultimate, Five, Jaguar and Electronic Arts.
Peter Riley, agency founder and creative director, said: "We've got so much new-business recently that it's imperative we have Maggie to develop long-lasting relationships with new and existing clients."
At Space 01, formerly Brandsalt, Lonergan was client services director for two years after moving from the same position at eMC Saatchi, which was folded into M&C Saatchi's direct marketing arm Lida. She has worked with clients such as Friends Provident, British Airways and Royal Bank of Scotland.
Lonergan said: "It's an exciting time for integration, and there is enormous potential for 20:20 as more clients look to innovate."
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