The stake is in exchange for services in kind. CHI & Partners is being paid for its work, has not invested any cash and has not committed to a set period of time or number of campaigns.
The shop will help relaunch Freedom’s brand identity and handle creative, social, digital and packaging design activity.
CHI & Partners has taken a share of the brewery so that it can "assume true creative ownership of the brand’s positioning and direction", according to chief executive Sarah Golding.
It is the agency’s first investment of this kind but Golding said she expected to "do more of this in the future, as we are an independent business with an entrepreneurial mindset".
Freedom chairman Stefan Turnbull said he chose an agency that could make it "famous" and help grow sales and distribution.