MEC’s digital division won the business following a four-way competitive pitch against the incumbent and other undisclosed agencies.
MEC already handles the remainder of the digital planning and buying business for Gocompare.com, as well as its offline spend.
Harvest Digital still handles the PPC search business, which was not part of the review.
A spokeswoman for MEC said: "The key objective of the account is to grow the volume of quotes generated at Gocompare.com through the online display channel."
In December, the advertiser launched a series of radio ads in the run-up to Christmas, featuring 'Peep Show' star David Mitchell.
The ads formed part of the long-running "Gio Compario" campaign, which involves an Italian opera singer warbling to potential customers about the comparison site.
Nick Hall, head of marketing at Gocompare, said: "MEC Interaction’s expertise was the perfect fit to support our already successful above-the-line advertising, and optimise the online audience."
Matt Dailey, business director, MEC Interaction, said: "This is a great opportunity to deepen our already successful partnership with Gocompare.com, who we have worked with on their above-the-line Gio Compario campaign."