The agencies won the business following a pitch handled by Agency Insight.
The agency will now take responsibility for producing traditional direct marketing as well as television and print ads.
The Omnicom-owned incumbents DDB and WWAV Rapp Collins, which handled the advertising, DM and media accounts, declined to re-pitch.
Trinity Communications, which is part-owned by Kitcatt Nohr, will handle media planning and offline media buying, while i-Level will work on digital communications.
Pippa Carte, the acting director of supporter relationship management at WWF, said: "WWF is a key player in global conservation and our fundraising needs to keep pace with growing external challenges. To support this we wanted a mix of agency partners to deliver robust fundraising campaigns, grow our income, and our supporter base and broaden our audience reach."