The account was awarded without a pitch and the incumbent was The Gallery. Gumtree has also previously worked with Albion, which won a branding brief in 2008 off the back of an existing relationship with Gumtree's parent company eBay.
The Gumtree website launched in March 2000 in London and now covers more than 60 cities, and claims to be the UK's largest website for local community classifieds.
In April, it appointed AW Media as its first retained media agency to handle planning and buying for a press, outdoor and digital campaign.
Sam Taylor, the head of brand and marketing communications at Gumtree, said: "We're delighted to be working with Beta. It has shown an in-depth understanding of our business in a very short space of time."