The move reaffirms Ogilvy's leading position in the market and, by its own estimates, is now twice the size of its nearest competitor in China.
Based in Beijing, BrandOne will continue to act as an independent agency. It has 22 staff and clients include Northwest Airlines, Digital China and Yahoo!.
Paul Hu who was previously marketing manager in Beijing for Northwest Airlines, an OgilvyOne client, set up BrandOne in 1999.
Hu will report to Jennie Fan, national managing director for OgilvyOne China, who re-joins Ogilvy in May after a year studying in the USA. Fan was previously managing director of Ogilvy & Mather Advertising in Beijing and, before that, managing director of OgilvyOne in Taiwan.
The Ogilvy Group launched its direct marketing arm OgilvyOne in mainland China in May 2001. Sister agency Ogilvy & Mather has been active in China for 15 years.
It is the latest in a series of acquisitions for WPP in the region. Last year, Enterprise IG, the WPP-owned branding and identity consultancy, opened its first office in China, based in Shanghai.
OgilvyOne Worldwide is has 115 offices and is active in 55 countries. It has total billings of more than $1.6bn (£1.1bn).