OMG agency PHD has retained the US business, which was worth $457 million in 2012 according to Kantar, and will also run the Canadian and West African markets.
Group M agencies will manage the rest of the world, with MediaCom retaining the £60 million UK account. Dentsu will manage media buying in Japan.
Omnicom Media Group and Group M will share responsibilities for global category-planning for consumer healthcare, from London, the US city of Parsippany and Singapore.
The decision ends GlaxoSmithKline’s relationship with Publicis Groupe’s Starcom and Carat, which previously worked on the business alongside PHD and Group M.
Sam Singh, the vice president of global media at GlaxoSmithKline said: "The decision to consolidate our media investment with two network partners – Group M and OMG, with Dentsu buying in Japan, is based on various factors including simplicity and speedier deployment of best practices.
"We believe this sets us up with a fit for purpose media system into the future.
"We continue to hold the outgoing agencies, Starcom and Carat, in the highest of regard. They have consistently exhibited high levels of professionalism and we wish them all the very best."