OMD will now handle all of PepsiCo's planning on its beverage brands, as well as buying for its beverage and food businesses.
Bellamy Hayden, the Australian media company, which has an office in Bangkok, will handle the remainder.
The account was previously split between MindShare and OMD.
The agency decided to review its business in December last year in a bid to consolidate its beverages and food accounts in the country.