RKCR/Y&R won the account after a pitch process against undisclosed agencies.Primelocation.com previously handled all of its creative work in-house.
The agency's work for Primelocation.com is expected to launch in March 2009.
This initial integrated activity will focus on building on Primelocation.com's profile with property buyers and will aim to encourage online property browsing during the housing market slump.
RKCR/Y&R will launch a larger brand campaign later in the year when it is hoped the property market will start to recover from the effects of the economic downturn.
Last week, Primelocation.com reported that property prices had increased by an average of 1.3 per cent in top London locations in January.
Richard Exon, the chief executive of RKCR/Y&R, said: "Primelocation.com has carved a position as the strongest name in property search for the top end of the market."