The deal, first announced in October, last year, will see Ebay merge Motors.co.uk with its other consumer-facing car sales business Gumtree Motors.
The CMA said at the time of launching its probe in December that it had feared a "substantial lessening" of competition in the sector as a result of the merger.
The tie-up will create a combined group of Motors.co.uk, Gumtree Motors and Ebay Motors, which will offer more than 620,000 car listings across the sites and reach more than 10m unique site visitors. The move blows its next largest rival out of the water, as Auto Trader manages roughly 500,000 listings.
Cox Automotive, which currently owns Motors.co.uk, entered into a joint venture with Auto Trader last year to create a new online auction service called Dealer Auction.
A Gumtree UK spokesperson said: "We welcome today's decision by the Competition and Markets Authority (CMA) to approve Ebay’s proposed acquisition of Motors.co.uk from Cox Automotive. Subject to satisfaction of all closing conditions and upon deal closing, Motors.co.uk will become part of Gumtree UK, an Ebay Classifieds Group business.
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