The firm beat eight agencies to take the retained brief, which had been held by Cow PR since late 2013.
Well Hello will deliver editorial and creative content across a range of business areas, from online doctor services to sexual health, intimate health, smoking cessation, diet and fitness and beyond. It will be led by Well Hello co-founder Lisa Taylor, who left her role as MD of Cow PR in November.
The first superdrug health and wellbeing store was opened in 2014, the second in 2015, and further stores are set to open in future.
Superdrug operates more than 200 pharmacies and the retailer recently announced operating profit of £62.2m for the year ending December 2015, up from £38.3m in 2014.
It is the biggest win to date for Well Hello, whose other co-founder Nick Woods was formerly the deputy general manager for the UK at WE Communications, previously Waggener Edstrom.