It follows a review that was called in February that was handled by Chris Nolan, media and digital director for Kellogg EMEA.
Carat has held the European business since 2008 when it won the account from Mindshare, which had held it for eight years.
DigitasLBi worked with sister Publicis Groupe agency Leo Burnett, Kellogg’s creative shop, to pitch for the business in order to "demonstrate the need for a seamlessly integrated agency team with data and digital at its heart".
The agency described this as the group’s "power of one" approach, a strategy that was used to win the Shangri-La account.
Nolan said: "Importantly for us, [Carat and iProspect] also showed a commitment to drive media forward with a vision and a plan for how we will develop across the next three years.
"DigitasLBi demonstrated a deep understanding of how digital can drive our business forward. They understood the need to put data at the heart of what we do and to drive change in how we connect with our consumers into the future.
"Their approach to integration is simple and compelling, and we believe our brands will benefit from it immediately."