The business involves activity across European markets, but will be controlled through the main MPG Paris office.
The move will help Citroen with pan-European planning and buying, but will not affect local territory work. OMD still retains the £76m PSA Peugeot Citroen account in the UK, after retaining it in a battle against a consolidated bid from MPG and Group M in the form of 2MV.
The agency managed to pick up the PSA Peugeot Citroen account from OMD in two territories, Spain and Germany, but lost the account to OMD in its French homeland.
Yves Del Frate, MPG's global brand manager for PSA Peugeot Citroen, said: "It is this track record within the brand portfolio that has led to a deep understanding of Citroen's brand strategy.
"With this history, we are ideally placed to continue to offer insightful and effective communications solutions.
"I am also pleased that our ability to offer a network specifically organised to harness multi-market synergies is being leveraged by this respected client."
Jean Marc Savigne, head of advertising for Citroen Europe, added: "Citroen has undertaken a specific approach to managing its markets.
"It is clear to me that Citroen's emphasis on marrying strategic synergies with insightful local market intelligence links with MPG's approach to marketing communications."