Walsh Trott's brief is to develop a campaign to celebrate the chain's 40th birthday, expected to run in the spring.
Although the campaign is understood to be a one-off project, it is expected that the agency will be appointed to the retailer's entire advertising account in due course.
Murray Chick, the chairman of Walsh Trott Chick Smith, said: "This is a great win for the agency and a fantastic start to 2004."
Superdrug has been without an above-the-line agency since it parted company with Bates in 2002. Its most remembered work were the ads that broke in 1996, featuring customers' video diaries.
This was followed by a national press and television campaign in 2000 to launch its make-up brand, Kolor.
Liza Fenwick, Superdrug's advertising and promotions manager, said: "We were impressed by WTCS's energy and ideas and look forward to a successful campaign."
Superdrug's media planning and buying is handled by ZenithOptimedia.