Agency Republic will be responsible for digital work including social media activity for the charity's innovations team to recruit new donors.
The agency will work with the team to help drive new ways of thinking in a bid to target new audiences.
Agency Republic joins a roster of agencies that includes Abbott Mead Vickers BBDO, Rapp, Rapier and The Good Agency.
Recent activity from the charity included an emotive ad campaign that asked supporters to pledge £2 a month. The "couples" spot was created by AMV and featured mothers, daughters and husbands talking about their loved ones' lives with cancer.
In April, Cancer Research hired AnalogFolk to handle a campaign to promote its celebrity event, "The Swim".
Agency Republic declined to comment.