The agency landed the accounts without a pitch after being appointed to handle the Mini Babybel business, which is also owned by Bel Fromagerie, in January. It will now create TV and print advertising to run across Europe.
Boursin has used Publicis in the past to create its advertising, but the brand has not developed any new creative in the UK for 15 years.
The incumbent on the Leerdammer account is Saatchi & Saatchi, which won the EUR80 million (£63 million) pan-European Babybel, The Laughing Cow, Leerdammer and Port Salut accounts in 2004.
Bel Fromagerie's marketing director, Ian Greengrass, said: "Our brands are premium yet accessible, and, in RKCR, we found an agency which understood the balance between the two."
Tony Harris, RKCR's chief operating officer, added: "People are more open to exploring brands like Boursin and Leerdammer than ever before."