The agency won the business following a pitch against PHD Rocket, the incumbent.
It already works with Coca-Cola Great Britain, which owns a minority stake in Innocent.
The agency will now handle planning and buying for the company's entire product range in the UK, which includes Squeezies and Veg Pots as well as smoothies and drinks lines.
In March this year, Innocent appointed Fallon to handle its advertising business.
The agency beat WCRS in the final round after VCCP pulled out at an earlier stage.