The agency takes over the work from Leo Burnett, which resigned the business in May, following a disagreement over future strategy.
Nintendo UK marketing director Dawn Paine said: 'We are delighted to appoint a dynamic, creative but unbureaucratic agency that puts the client's commercial and creative requirements ahead of ego and process.'
Karmarama, which has been hired on a project basis, has been briefed to continue the brand's strategy of targeting the non-traditional gaming community, such as older players and women. Its first task will be to develop a Christmas ad campaign.
Nintendo has successfully used the non-core gamer approach to back the launch of its handheld DS and Wii console last year. However, it now faces competition from rivals such as Microsoft, which is also set to target a wider audience (Marketing, 4 July).