The integrated agency has been called on to create effective social-led campaigns to support key initiatives such as the charity's Race for Life and additional social brand activity.
A spokeswoman for the agency said the agency is the only one handling social media for the charity, and that the contract, which was won following a four-way competitive pitch, is held on a rolling basis.
Cancer Research UK had stressed to agencies the importance of co-creating campaigns with their supporters. Brand, marketing and comms director Anthony Newman said: "Good Agency understands the importance of putting our supporters, fans and followers at the forefront of our work. We’re confident this partnership will strengthen our connection with our online audience and increase support behind our life-saving strategy."
Working alongside Cancer Research UK’s in-house social team, Good Agency’s dedicated team of planners, community managers, designers and videographers will create social campaigns for key channels to mobilise the online target audience.
Chris Norman, strategy director for Good Agency, who will work alongside the charity's in-house social team, said: "We both believe that social has enormous potential to inspire support and participation."
The agency was appointed to the charity's strategic and tactical design roster in May this year.
The charity had an income of £665m in the year to 31 March 2015. It has 223,000 followers on Twitter and 1.2 million likes on its Facebook page.