The agency has been hired following a pitch to help develop a campaign that will launch in October and is backed by organisations such as Debenhams, the Government Equalities Office and YMCA.
The three-year brief will initially involve Forster looking to develop a brand and identity for the Campaign for Body Confidence, positioning it as the authority on body confidence and establishing body image anxiety as a national public health concern.
Forster director Peter Gilheany said: "You’d be hard pressed to find someone who doesn’t think we should be more confident in our bodies and yet there is this sense of powerlessness in terms of it becoming more of a social challenge.
"Tackling an issue as insidious as this one will require long-term thinking, with one of the challenges being getting the coalition partners unifying behind an inspiring set of messages. Once that is done, it will be about maximising the reach and influence of those organisations."
In 2012 the All Party Parliamentary Group on Body Image released details of a YMCA-commissioned study into the causes and consequences of body image anxiety.
MPs polled highlighted celebrity culture (68 per cent), the fashion industry (53 per cent) and advertisers (52 per cent) as the three elements most responsible for the British public's negative feelings about their bodies.
Denise Hatton is CEO of YMCA England, which is co-ordinating the coalition’s efforts. She said: "With more than half the UK’s population now suffering from body image anxiety, the issue is rapidly becoming a pressing and growing concern across society.
"Given the scale and size of the challenge we face, the coalition recognised the need for an agency equipped with the skills and experience to bring about genuine social change."