The account was previously held by LD Communications.
W will manage PR across the entire project, deliver a series of campaigns to mark the festival's 10th birthday and provide a full on-site publicity team during the three-day festival in Finsbury Park.
Wireless promoter Steve Homer of Live Nation said: "W impressed us with its creativity and energy, matched with a sound understanding of the New Look Wireless offering and of the media. It delivered a refreshing and imaginative strategy that we are confident will help drive footfall to the festival and continue to raise the profile of the Wireless brand for its 10th birthday."
Warren Johnson, W founder and CEO, added: "Live Nation is the largest live entertainment company in the world, so it is incredibly exciting to be working with it. Wireless has an amazing reputation for breaking and nurturing some of the biggest names in global entertainment and it will be an excellent addition to our thriving entertainment division."
This year's headliners include Drake, Avicii, Nicki Minaj and David Guetta.