In her new role, Chapman will work on the Department of Health's anti smoking campaign as well as the Debenhams and Premier Foods accounts.
Chapman, who will report into planning director Andy Nairn, has spent seven years working in Australia, where she also worked at BBDO and Publicis.
In her last role, Chapman was planning director and co-founder of the Mojo group agency Hive.
Prior to Hive, she spent two years at Abbott Mead Vickers BBDO, working on Sainsbury's and Road Safety campaigns covering issues such as drink driving, the wearing of seat belts and mobiles phones.
Nairn said: "I am delighted that we continue to attract some of the best planning brains in London. Helen is a great hire and illustrates our commitment to hiring quality experienced best-in-class planners."