The move displaces longtime partner Wavemaker, which has had a stronghold on the business since 2014.
The brand has already in-housed chunks of its digital planning and buying, but was looking to appoint a single agency to handle the remaining portion of the operation.
Carat will now take the lead in key markets like the UK, Germany and Italy when it comes to offline buying. It will also advise on in-sourcing digital.
Will Swayne, chief client officer of media and performance at Dentsu Aegis Network said: “Vodafone is a future-focused organisation, challenging old ways of doing things while pioneering the new and maximising the opportunities of the digital economy.
"We are delighted to be partnering with them, integrating the best of our agency capabilities to accelerate Vodafone’s evolution to become market-leading in digital marketing and in-house media buying.”
Wavemaker originally won the brief five years ago as MEC prior to its merger with Maxus. Since that time, Vodafone has internalised a "significant" portion of the business.
In July it was revealed that Sara Martins de Oliveira, the marketer who has been spearheading Vodafone's shift towards an in-house digital media model, was to step down from the firm.
Though news of her departure dovetailed with the media pitch, it's understood she has seen it through to its conclusion.
Under Oliveira's watch the brand has in-housed biddable media, including search and social. Her experimentation means it now has internal digital teams serving 11 of its 25 markets.
A Vodafone spokesperson said: “After an extensive process Vodafone Group has chosen to appoint Dentsu Aegis as our new global media planning and buying agency."
They added, "Dentsu Aegis has strong credentials to support Vodafone, particularly with regards to its experience supporting other clients who have moved digital media buying in house.”