The commission had raised concerns that the deal would damage competition because it swelled WPP's media buying power by adding MediaCom to its existing media networks, Mediaedge:cia and MindShare.
It asked WPP for more information concerning how the merger would impact competition in key markets, particularly Germany, and launched a one-month merger review process.
The EC ruled there are more than enough rivals to challenge WPP and ensure a competitive market, and in a statement it said that "after detailed analysis, the commission has concluded that the merger would not significantly impede effective competition".
"There were many strong competitors remaining and therefore there was no risk that the creation of the new entity would bring about a significant impediment to competition," it said.
The deal had originally been due to conclude in January although there were never serious fears that the EC would block the deal or impose conditions on it going through, which it has the power to do so.
It could have forced WPP to sell off MediaCom offices, particularly in Germany where the group is strong.
WPP's media dominance increased towards the end of last year following its win of several major media accounts including the £680m pan-European Unilever win.
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