The agency picked up the business following a pitch against a number of undisclosed agencies.
Innocent is planning a series of promotions this summer, culminating in a "village fete" in Regent's Park in August.
Soup has been initially briefed with creating a website that will back the event, and will also promote the overall concept of the village fete as a British pastime.
As well as providing information about the Innocent event, and other fetes nationwide, the site will also support an online community dedicated to fetes.
The Regent's Park event will have unsigned bands, comedians and theatre groups, as well as cake stands, wellie wanging and coconut shies.
It represents a change in direction for the company, which has recently invested its summer promotional budget into a one-day music festival called Fruitstock. However, Innocent decided to stop running the festival in favour of smaller events.
Innocent now has a 68 per cent share of the smoothies market, with an annual turnover of £100 million.