The account also includes the IAG Cargo and Avios brands which are also owned by International Airlines Group.
In a statement, BA said it was looking for a "transformational model to streamline a number of its marketing services" and that WPP delivered the best solution to the brief.
WPP will now manage media planning, strategy and buying, creative services, social media, paid search, affiliates and production for British Airways.
The world’s biggest advertising company will also manage Avios' media services and IAG Cargo's production and creative/studio work.
Campaign revealed on Friday that WPP had won the business, ending BA’s 12-year relationship with Bartle Bogle Hegarty. BBH had added the loyalty business to the ad account in 2014 following a review.
It is understood that Ogilvy will handle the advertising and loyalty accounts respectively, working with Group M on the media.
BA and sister brand Iberia awarded Carat their combined media account in August 2013. Carat has retained global media planning and buying for Iberia and added Vueling's business for all off and online media. Dentsu Aegis was awarded the global integrated media planning, buying and social account for Aer Lingus, another IAG brand.