Google did not deny the allegations and the fine was ordered as part of a settlement, according to the regulator on Monday.
Google has agreed to adjust its activities, a move accepted by the authority.
“We will be testing and developing these changes over the coming months before rolling them out more broadly, including some globally,” Google said in a statement.
The competition authority accused the company of abusing its dominant position in the ad server market, after complaints from several publishing groups including News Corp and Figaro, a French publisher.
One area they were disadvantaged is supply-side platforms (SSPs), an interface between website providers and advertisers where companies manage their online ads.
Google’s ad-brokering business made up 13 per cent of parent company Alphabet’s revenues of nearly 183 billion dollars last year.
“The authority found that Google has granted preferential treatment to its own technologies offered under the Google Ad Manager brand,” it said.
Google acquired advertising specialist DoubleClick in 2009 then ran a platform for advertising placements called DoubleClick for Publishers under the Google brand.
Many large online publishers and publishers use the platform to offer ad space for sale.
The companies complained that Google customers were given an advantage in the actual allocation of advertising space at the Google Ad Exchange (AdX) ad auction house.
In some cases, Google customers also had access to information about rival bids.
Its practices were “particularly serious” because those placed at a disadvantage include press associations whose economic model has already suffered serious attrition due to falling numbers of newspaper subscriptions, the regulator said.
The French regulator said companies with a position like Google have a particular responsibility. “These very serious practices disadvantaged competition in the emerging online advertising market and allowed Google not only to maintain its dominant position, but to expand it,” said Isabelle de Silva, who chairs the authority, in a statement.
“While we believe we offer valuable services and compete on the merits, we are committed to working proactively with regulators everywhere to make improvements to our products,” Google said.
“Over the past two years, we have been working with the French Competition Authority to answer their questions about our advertising technology, and more specifically about Google Ad Manager, our publisher platform,” the company said.
It remains unclear whether and how the settlement will affect other markets, where complaints have also emerged about the DoubleClick platform.
The requirements under the settlement are likely to become a form of template that publishers in many other countries can demand, experts say.