Germany is WPP's third largest market after the US and UK and is "showing signs of strength", according to company.
Commarco employs more than 1,200 people in its offices throughout Germany, Switzerland and selected international markets. Its clients include American Express, Commerzbank and Credit Suisse.
Last year Opel, the General Motors-owned car manufacturer, appointed Hamburg-based Scholz & Friends to handle its pan-European advertising account.
Other Commarco companies include integrated agency deepblue, relationship marketing agency, gkk DialogGroup and production agency United Visions.
Gross revenue for the company was £132.9m for the year ended 31 December 2010.
The deal is subject to regulatory approval.