Manifest becomes Gumtree's first retained PR agency since it parted company with 3 Monkeys Communications in 2013.
The appointment follows a link-up earlier this year when Manifest promoted Gumtree's sponsorship of Channel 5’s Celebrity Big Brother show.
The agency’s new remit will cover all external comms for Gumtree including the celebration of its 15th anniversary. It will also handle PR for Gumtree Motors, the private car marketplace.
Manifest will develop creative campaigns, co-ordinate all media and blogger relations and produce multimedia content of the UK's largest classifieds website.
Alex Myers, director at Manifest London, said: "The breadth of the Gumtree brand is every creative agency's dream. We're thrilled that Gumtree has chosen to build upon the successful relationship we started with the Celebrity Big Brother campaign. As one of the most visited websites in the UK, Gumtree is in a unique position to shake up the way we buy and sell, especially on our mobiles."
The account win comes after a year of growth for Manifest London, which saw the agency pick up new briefs from Samsung, Hailo, Durex and the MTV Staying Alive Foundation, Wild Geese Whiskey and NBC Universal.
Hannah Wilson, head of marketing at Gumtree, said the company had been impressed with Manifest’s activity throughout the Celebrity Big Brother campaign.