The agency picked up the brief after beating EHS Brann, also a Barclays roster agency, in a pitch.
The new reward scheme is understood to offer incentives to consumers every time that they use their Barclaycard but full details have yet to emerge.
Rapp was first awarded a place on the Barclays roster in August 2006, when the bank split its £15 million direct marketing account between the agency and EHS Brann.
In January 2008, Balloon Dog and Vital were also appointed to the main DM roster.
Rapp currently looks after all of Barclay's personal and premier banking services, as well as its savings and investment schemes.
It is also responsible for the bank's loans and mortgages accounts, and works closely with Barclay's ad agency agency Bartle Bogle Hegarty on its sports sponsorship activity, which includes the sponsorship of the Premier League.
Rapp's appointment is not thought to affect EHS Brann's existing relationship with Barclays. The agency works on the bank's planning and strategy, as well as on the development of Barclay's Goldfish account, an incentive-based credit card business that the bank acquired from Discover Financial Services in the U.S for £36 million in February 2008.