The agency won the business after a final shoot-out against i-level. Agencies including Starcom, Media Contacts and Agency Republic were knocked out at an earlier stage of the process, which was co-ordinated by Billetts.
Starcom continues to handle Capital One's offline media planning and buying business. Capital One previously handled the bulk of its online planning and buying in-house.
Last year, Capital One appointed WWAV Rapp Collins to handle its direct and digital creative work. This followed the selection of WWAV's sister agency DDB London to handle creative for the credit card company.
A Capital One spokeswo-man said: "We can confirm that we have appointed Zed Media to handle digital planning and buying."