Karmarama, which was acquired by consulting giant Accenture in November, won the work in a competitive pitch against Anomaly and Havas London. The incumbent, J Walter Thompson, did not repitch.
Philadelphia invited agencies to pitch a strategic idea for the brand that would work across the brand’s key European markets of the UK, Italy, Germany and Spain.The first work is expected to land in April or May.
Zoë Cashin-Howe, Philadelphia equity marketing manager, said: "Karmarama gave us confidence through their fresh-thinking approach to a compelling communications platform which could explode into powerful creative working across multiple countries and cultures."
It is the second time the account has moved from JWT in four years.
Philadelphia handed its account to Bartle Bogle Hegarty in 2013 after working with JWT since at least 1996. But the new relationship came to an end after just one campaign. After initially deciding to take the work in-house, Mondelez reappointed JWT in March 2015.
Jon Wilkins, executive chairman at Karmarama, said: "We are thrilled to have the opportunity to work with one of the world’s leading global brands across multiple markets to offer the best modern creative work throughout the customer experience."
Reports last year suggested that Mondelez was set to sell off Philadelphia, along with a number of other grocery brands.
Last week the food company agreed to sell most of its Australian and New Zealand grocery business - which includes yeast spread Vegemite - to Australia's Bega Cheese for A$460m (£280m). But the deal did not include the licence for Philadelphia.
UK sales of the cream cheese fell 8.4% last year to £94.7m, according to Nielsen.