W+K won the business following a pitch that kicked off in October last year.
The network, which is owned by Chinese telecommunications group Hutchinson Whampoa, previously used Glue Isobar to handle its advertising business. The agency did not repitch for the account.
Wieden +Kennedy will conceive and oversee the implementation of integrated campaigns and delivery of TV, radio, press, outdoor and digital advertising work.
The agency will work with a core team at Three to deliver a communications strategy for Three over the coming 12 to 18 months.
The first campaign is expected to appear in the first half of this year.
Margaret Burke, director of brand and integrated communications at Three, said: "W+K is a great match for Three, both in terms of their creative thinking and the way in which they can integrate a company’s brand story into their work."
Glue Isobar first won the advertsing business in December 2008 to add to its digital remit for Three.