Zibrant LIVE, which was awarded the contract following a multiple-agency pitch, will deliver Three's incentives programme to its employees in the UK and India.
Emma Coleman, account director, Zibrant LIVE, said: "I’m absolutely delighted that we’ll be partnering with Three for its incentive programmes.
"I’ve been working with Three for the last five years and it’s fantastic to be continuing my relationship with the team."
Commenting on the appointment, a representative from Three’s internal events team said: "We are excited to be partnering with Zibrant LIVE to deliver our overseas incentive events.
"Our challenge is to keep delivering amazing events for our staff and we believe Zibrant LIVE is the right partner to take us to the next level".