The ruling leaves the way open for the deal to be completed as early as March, providing it meets with the Grey shareholders' approval.
The European Union regulators had requested extra details on how the acquisition would affect competition in key markets, particularly Germany, where it was believed that the deal would give WPP an overwhelming amount of power as a buyer.
However, the regulator concluded the sale of Grey to WPP, which will produce the world's largest media buying outfit with a combined revenue of more than $1 billion, would not present a risk to the competition.
Separately, WPP is merging its Ogilvy Healthcare and Healthworld Communications Group to form Ogilvy Healthworld, which will become the world's largest healthcare communications network providing integrated consumer and professional marketing services.
Steven Girgenti becomes the chief executive of the newly combined company.
The merger coincides with the capture of two global brand identity accounts for AstraZeneca and Roche.
Ogilvy Healthworld will develop a brand strategy and marketing communications for Herceptin, Roche's targeted breast cancer therapy.