The two Omnicom agencies teamed up to defeat the incumbent, Proximity, and Saatchi & Saatchi in a three-way pitch. The original short-list also included Claydon Heeley Jones Mason, and the team of Ogilvy & Mather and Ogilvy One.
The media account, which was held by Proximity, will now go to OMD Connect - the joint media venture between WWAV and OMD.
WWAV and BMP will now begin work on both a fundraising and a repositioning campaign, designed to raise awareness of the threat posed to the environment from climate change and the effects of toxic chemicals.
Robert Mayes, the group communications director for WWAV Rapp Collins Group, said: "WWF has a vital role to play in helping stop the degradation of the planet's natural environment. WWAV and BMP will be working closely together to integrate WWF's brand and fundraising efforts and thus ensure the brand works to its full potential.
"By highlighting the environmental issues we're all facing and increasing awareness of the brand in relation to this, we are confident we can maximise WWF's fundraising."
The win does not affect WWF's international creative account, which is held by Ogilvy & Mather. The agency recently created a global print campaign for the charity, which aimed to convince the banking and finance community to think again before supporting large dam projects.
Proximity will continue to work with WWF until September.