The agency won the business following a five-way pitch against Abbott Mead Vickers BBDO, DraftFCB, Bartle Bogle Hegarty and Leo Burnett. The incumbent, DDB, did not repitch.
RKCR/Y&R will now work on ads for the charity's UK campaigns, and support its relief work around the globe.
Cathy Ferrier, Oxfam's fundraising and supporter marketing director, said: "We were extremely impressed with the agency's response to the brief and their commitment to Oxfam's mission."
Richard Exon, the RKCR/Y&R chief executive, added: "The scale and ambition of Oxfam's cause is awe-inspiring. We're proud to be moving forward as Oxfam's partner."
In July, Oxfam hired Leo Burnett to handle advertising for Oxfam Unwrapped, and in August, it appointed ZenithOptimedia to its media planning and buying account.