The Hertfordshire-based agency will manage the two-day roundtable conference for the UN Environment Programme - Finance Initiative.
Rather than tendering for such a high-profile event, the appointment came about through a series of discussions over time between the two parties.
The event runs annually, and has taken place on previous occasions in destinations such as Tokyo, Frankfurt and Rio de Janeiro. This will be the first time that full support has been given by an outside agency.
"We are absolutely thrilled to be working for such a prestigious client and with a subject matter that affects all of our lives," said project manager Neil Pace. "The UN decided it wanted to give the event a bit of a lift, which is what we do best."
As the world's principal event on sustainability in the finance sector, it will attract over 500 leading professionals and government officials from around the globe.