The move brings the credit card specialist's digital media account under the same roof as its offline media planning and buying business.
The US-headquartered group first entered the UK in 1996 and is now a top 10 credit card issuer. The company also offers personal loans, homeowner loans, mortgages, insurance and savings accounts.
MediaVest declined to comment but Capital One admitted it has reviewed its digital media model and decided to "consolidate our display advertising with our existing above the line media agency".
The company also stressed it has enjoyed working with Zed but has also moved "significant elements of the business", previously handled by the digital specialist, in-house, including aggregators and affiliates.
According to figures from Nielsen Media Research, direct mail made up the bulk of Capital One's £17m media spend in 2008, despite the company slashing its DM activity from £36.9m in 2007 to just £6.4m for the 12 months to 31 October 2008.
Last May, in a parallel with this week's media account move, Abbott Mead Vickers BBDO picked up Capital One's £15m creative business from Omnicom sister agency DDB London without a pitch.
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