EHS saw off competition from Clark McKay & Walpole and Kitcatt Nohr Alexander Shaw.
The agency will produce direct mail and press work for the charity, which helps reduce suffering and extreme poverty in developing countries.
EHS Brann will be tasked with developing two to three campaigns a month including regular donor mailings, upgrade and conversion mailings, as well as offering broader planning advice and ideas over a three-year period.
The charity, which has not previously used direct marketing, will also brief the agency to produce emergency campaigns based around humanitarian crises like the Asian Tsumani.
Concern's head office is in Dublin, but it has three regional offices in the UK in London, Edinburgh and Belfast.
In the Republic of Ireland one out of ten households donates to the charity, so EHS Brann will focus on upgrading givers to a new level of support in the country.
In the UK, where awareness of Concern is low, the campaign will focus on an acquisition strategy.
The agency's data arm, EHS Brann Discovery, will develop the charity's customer database and identify areas of opportunity.
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