WPP said its Kantar Consulting arm had acquired Mash Strategy, a London-based brand strategy and growth consultancy, for an undisclosed sum.
Mash clients include Johnson & Johnson, Samsung, Unilever and PepsiCo, WPP said.
Founded in 2010, the company employs around 25 people in London and New York.
Kantar Consulting is part of Kantar, WPP's data investment management division.
At 9:38am: (LON:WPP) WPP Group PLC share price was +13.5p at 1337.5p