The appointment sees the account moved out of long-standing agency EHS Brann, which held the brief for eight years. The work was originally won by Brann, which held on to it following its merger with EHS:Realtime.
The review was called in October, with the pitches taking place in January. EHS Brann was invited to pitch, although the charity refused to be drawn on whether any other agencies were involved.
A spokesman for the charity said Proximity's brief will include developing campaigns using direct mail, press, press inserts and door drops.
"Proximity London will work with Save The Children UK to develop a more supporter-focused approach. The work will include a range of direct marketing activity to retain current supporters and acquire new donors," the spokesman said.
The contract has initially been awarded to Proximity for one year. It follows a review in 2001 of the charity's above-the-line account, which was awarded to Catalyst. Its media work is handled by Feather Brooksbank.
"Both organisations envisage the partnership will develop over time in the context of the broader marketing strategy," the spokesman said.
EHS Brann will continue to work with the charity until October.
EHS Brann's work for the charity included a national press campaign, which focused on the link between poverty and child prostitution using the line: "Rachael is so poor she has to sell herself."
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