Umpf won a four-way pitch to manage the account and will help promote activities throughout 2015 to celebrate 100 years since the WI’s first UK meeting in 1915.
Umpf will also run creative campaigns to celebrate the history of the organisation and raise awareness of the organisation's work today.
The agency will work with the WI on a number of online campaigns to directly involve members in the celebrations.
Pip Morrall, account director at Umpf, said: "The WI is an iconic and important British institution so we are honoured to be involved in telling its story during its centenary year. We can’t wait to kick off all our campaigns and tell the WI’s story in new ways and potentially to new audiences."
Charlotte Fiander, head of comms for the NFWI, said: "It is rare that any organisation has such an opportunity to celebrate its past and look to its future, so we are incredibly excited to share our centenary year with our members as well as the wider public, and open more people’s eyes to what the WI is really about.
"We chose to work with Umpf as we were impressed with its creativity and approach. We’re hoping that through this partnership we can communicate the WI's history in new ways and ensure we maximise all the opportunities that our centenary year brings."