Mediapool, Estonia's second largest media agency, has a number of domestic and international clients, including SEB Bank and Nissan.
Aegis already has an operation in Estonia with Carat, and the agency now plans to introduce its sister agency Vizeum into the Baltic region.
Robert Lerwill, chief executive officer at Aegis, said: "This acquisition makes good sense on three clear counts. First, Mediapool is a very successful business in its own right. Second, alongside Carat, it will build our scale and capability in the market. And finally, Mediapool is the ideal platform to launch Vizeum in the Baltics."
Earlier in the week, Aegis Group acquired Dutch digital and direct marketing agency Bookmark, which has assets of €1.4m, as part of its Isobar network.
The sale of Mediapool is expected to be complete by the end of August.
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