WPP-owned MediaCom beat Dentsu-owned Vizeum, Publicis Groupe's StarcomMediaVest Group and sister agency MEC to the business.
The WPP media agency will now take on the UK planning and buying for all Coca-Cola brands including Diet Coke, Coke Zero, Sprite, Fanta and Oasis.
Jon Woods, managing director of Coca-Cola Great Britain and Ireland, said: "After our recent media review, we can confirm that we have appointed MediaCom to oversee our media planning and buying business in the UK.
"The appointment will be effective from July 2013. We would like to thank Vizeum for their high quality work over the past 12 years. They have been a true, collaborative partner and we are grateful for their expertise."
The move is a blow to Vizeum as it and its predecessor agency BBJ has worked with Coca-Cola for 12 years. It added the media buying business to the planning account it already held in November 2007.
Prior to consolidating the account in 2007 Coca-Cola’s buying was handled by Interpublic agency Universal McCann, which was involved in the 2007 pitch alongside Starcom and Naked Communications.
Last year much of Coke’s marketing centered around its partnership with the 2012 London Olympic and Paralympic Games but this year the company’s brand marketing has been notable for tackling the issue of obesity.