GoCompare.com is in advanced talks about awarding its media buying account to Omnicom's Hearts & Science, according to a spokesman for the price-comparison brand.
Carat was the incumbent and has handled the account since 2011.
GoCompare told investors earlier this year that it is investing in "smarter marketing", including building its in-house media planning capabilties, to improve "efficiency" and "speed".
Zoe Harris, former chief marketing officer at Daily Mirror owner Reach, joined the company as chief marketing officer in the autumn.
GoCompare said in its annual report that it spent £88m last year on marketing costs, but it did not disclose its media buying spend, which is estimated to be in the region of £40m.
The company said "improving the efficiency of spend has been a key area of focus", after de-merging from Esure Group in 2016 to become a stand-alone business.
A Carat spokesman said it chose not to participate in GoCompare's review, adding: "We wish them well with their new agency."