What You Need to Know

• A US District Court has ruled Google’s ad tech stack an illegal monopoly, finding it abused market power across publisher ad servers (DFP) and ad exchanges (AdX). Google will appeal.
• Judge Leonie Brinkema said Google “willfully” dominated by tying AdX to DFP, locking up 90% of the global publisher ad server market and over half of ad exchange transactions.
• This follows last year’s ruling that Google also maintains an illegal search monopoly, highlighting US courts' growing willingness to curb Big Tech.
• Remedies, including potential forced divestiture of DFP and AdX, are being hammered out; first rulings expected around August, with appeals likely.
• Analysts warn of higher counterparty risk for publishers and brands, but doubt a breakup will occur quickly due to appeals and possible Supreme Court pushback.
• Brands, agencies, and publishers urged to diversify adtech partnerships, reduce over-reliance on Google, and expect increased auction transparency.
• The DOJ framed the decision as a landmark win against Google’s control of online advertising; Google maintains it offers superior, affordable tools and vows to fight on.
• Broader impact: The decision could spur antitrust actions globally, with Australian regulators like the ACCC eyeing similar moves.

In a bruising judgement with very significant digital advertising implications for brands, publishers and the adtech ecosystem, US District Court has ruled Google’s ad tech stack an illegal monopoly – smashing the search giant for abusing market power across two critical links in the digital advertising supply chain. Google has already indicated it will appeal.

US District Judge Leonie Brinkema’s 115-page ruling found Google "willfully acquired and maintained" dominance in both the publisher ad server and ad exchange markets – and it didn’t do it by building better tech. Instead, the court found, Google tied its powerful ad exchange (AdX) to its publisher server (DFP), effectively forcing publishers to adopt DFP to access AdX’s vast demand pool.

The strategy worked. Google locked down around 90 per cent of the global publisher ad server market and seized control of more than half of ad exchange transactions.

It’s the second hammer blow in under a year. Last August, as Mi3 reported, Judge Amit Mehta ruled Google a search monopolist, slamming the tech giant for stitching up default search deals with Apple, Samsung and others – deals that welded the competitive moat shut and froze rivals out.

This latest ruling cements a clear trend: US courts are increasingly willing to take the fight to Big Tech’s entrenched power. For Google – and for the digital advertising ecosystem – the dominoes are starting to fall.

As Mi3 reported last week, "The break-up actions – known in legal jargon as remedies – will be hammered out over the next three weeks. We may see the first rulings around August. There will then be appeals, though the court can rule that the break-up happens even while the appeals are being planned and fought."

Analysts flagged increased risks for market participants from the ruling, but also scepticism about the sustainability of the ruling. According to Forrester senior analyst, Nikhil Lai, "This ruling, along with Judge Mehta’s finding that Google maintains an illegal search monopoly, heightens [the already substantial] counterparty risk between Google and publishers and raises the likelihood of Google’s overhaul."

Lai added, "At least, Google will be compelled to not destroy evidence of its monopolisation going forward. Furthermore, Google could restructure by separating its ad server from its ad exchange, opening the loop between its AdTech. When we last surveyed US online adults about Google’s illegal monopolies, only 18% said they 'believe that Google will have to break up,' suggesting consumers’ realisation that any order to break Google up would languish in courts of appeals and, ultimately, be struck down by a sceptical Supreme Court.

"This ruling, along with Judge Mehta’s finding that Google maintains an illegal search monopoly, heightens [the already substantial] counterparty risk between Google and publishers and raises the likelihood of Google’s overhaul. At least, Google will be compelled to not destroy evidence of its monopolisation going forward. Furthermore, Google could restructure by separating its ad server from its ad exchange, opening the loop between its AdTech. When we last surveyed US online adults about Google’s illegal monopolies, only 18 per cent said they “believe that Google will have to break up,” suggesting consumers’ realisation that any order to break Google up would languish in courts of appeals and, ultimately, be struck down by a skeptical Supreme Court." 

Recent Supreme Court rulings suggest consumers have a point. In Loper Bright Enterprises v. Raimondo (2024) the Court overruled the Chevron doctrine, which had required courts to defer to federal agencies' reasonable interpretations of ambiguous statutes, shifting interpretative authority from agencies to the judiciary, potentially limiting regulatory oversight and favouring corporate interests. ​Then, in an 8-1 decision, the Court sided with Starbucks in a dispute over the firing of employees involved in union organising, making it more difficult for the National Labor Relations Board to obtain injunctions against alleged unfair labour practices. This ruling is seen as weakening labour protections and favouring corporate employers. And the 8-1 result suggests this has less to do with ideology and instead reflects how the current laws are drafted.

Spinning of out the gate

Both the DOJ and Google took to the town square after last week's judgement.

According to Assistant Attorney General Abigail Slater of the Justice Department's Antitrust Division, “The Court’s ruling is clear: Google is a monopolist and has abused its monopoly power. Google’s unlawful dominance allows them to censor and even deplatform American voices. And at the same time, Google destroyed and hid information that exposed its illegal conduct. Today’s opinion confirms Google’s controlling hand over online advertising and, increasingly, the internet itself.”

For its part, Google said it was partly vindicated by the ruling and that it would appeal. Lee-Anne Mulholland, vice-president of regulatory affairs at the search engine giant said, “We won half of this case and we will appeal the other half… Publishers have many options, and they choose Google because our ad tech tools are simple, affordable and effective.”

How we got here: Acquisitions, tying, and market locks

It is important to recognise the ruling isn’t simply about Google’s scale, vast though it is. At the heart of the judgement was a illegal strategy to use that scale. Google’s 2008 acquisition of DoubleClick handed it the crown jewel of publisher-side ad tech: The dominant ad server. From there, the tech giant built a data and distribution flywheel that became nearly impossible to unseat.

The US Justice Department case against Google over its advertising tech dominance represents a long-overdue unboxing of the search giant’s industrial-strength monopoly toolkit. Judge Brinkema’s diagnosis was emotive and suggests Google didn’t just build a better mousetrap, it rigged the game.

The court's finding reads like a how-to manual on tech platform overreach, and Judge Brinkema breaks the playbook down increasingly familiar moves.

• Step one, buy the Pipes: Google’s 2008 acquisition of DoubleClick wasn’t just about adding a few widgets to the ad stack. It gave Mountain View the pipes and the plumbing: DFP (for publishers) and AdX (its exchange). Infrastructure plus insight equals leverage. In one move, Google became both landlord and auctioneer.
• Step two, bundle the goods: Access to Google’s high-demand AdX inventory? Sure, but only if you also plugged into DFP, the dominant ad server. That’s not synergy, that’s a technical tether. The court found that integration wasn’t about efficiency, it was about control. One login to rule them all.
• Step three, tilt the playing field: AdX got to peek at bids before anyone else. In fact, it got the first look and the last look. Throw in pricing constraints on publishers and opaque rules for rivals, and you’ve got an ecosystem where Google always wins because it designed the game.

An internal memo, unearthed by the court, cut to the chase: Google knew it was winning because it “owned the platform, the exchange, and a huge network.”

Indeed, Google’s approach has been likened the setup to a major bank owning the stock exchange.

The court systematically dismantled Google’s legal defences. Its argument that ad tech is a single, two-sided market akin to credit cards (as seen in the Supreme Court’s AMEX ruling) was dismissed. Judge Brinkema found ad tech tools are complementary, not interchangeable, and thus deserve separate scrutiny.

Importantly, the court also rejected Google’s justification its integration enhanced security and efficiency. Instead, it cited older antitrust principles from cases like Microsoft, determining that any technical gains did not outweigh the harm to competition and consumers.

One bright spot for Google? The DOJ failed to prove monopoly in advertiser-side tools. But as much as Google leant into that small consolation, it was cold comfort, given the central charge stuck.

Strategic marketing implications

Assuming the ruling holds up under appeal, marketers and publishers should take note that the ground just shifted, even if ongoing legal shenanigans mean it’s shifting at a tectonic pace, for now.

With Google’s integration model ruled illegal, digital advertising’s power balance is in flux. For publishers, this could mean reclaiming some control. If remedies include interoperability mandates or a forced divestiture, it may become viable to plug into multiple ad exchanges without losing demand.

Expect media teams to vet new partners and reconsider their ad server strategy. Agencies, too, will likely revisit their supply path optimisation over the long term, wary of the risks of over-reliance on a now-legally compromised platform.

For advertisers, diversification is the new imperative. Hidden take rates and lack of auction transparency were tolerated under the assumption of efficiency. That assumption has been broken. Brands will be looking for alternatives, cost savings, and clearer reporting.

At least that’s the theory. But 30 years of ad tech practice suggest brands were surprisingly comfortable with the kind of Stockholm Syndrome economics that led to Google’s illegal monopoly in the first place. And until all the appeals have run their course, expect a degree of inertia. 

Could Google be broken up?

The most consequential fallout from the ruling, if it survives judicial review and America’s new tendency towards executive branch intervention, comes from the potential structural remedies that are on the table.

The DOJ wants Google to divest AdX and DFP, the very tech stack found to be illegally tied. A breakup would be the largest forced divestiture since AT&T’s split. The rationale: Remove Google’s ability to preference itself and let competition rise. In theory, the ruling should spur innovation and level the playing field.

Such a move could also drastically reduce take rates across the ecosystem. Take rates are the percentage of revenue an advertising technology platform retains from the total ad spend that passes through its platform. They are more commonly referred to as the adtech tax.  

And there are also risks. Programmatic liquidity could drop in the short term. And publishers fear disconnection between systems could hit fill rates and revenue. That’s why behavioural remedies such as interoperability mandates, auction transparency, and mandatory participation in header bidding may also be considered.

Googling hypocrisy

Google will appeal as is its right. But the precedent is set. The legal ruling gives other jurisdictions such as Australia, Europe, and parts of APAC, new momentum and global regulatory pressure to intensify.

In Australia, where the ACCC has voiced similar concerns, this decision could trigger fresh scrutiny or reform. Regulators now have judicial validation to push for transparency and structural reforms.

And a final irony: The US administration finds itself defending the monopolistic consequences  of illegal behaviour by US platforms, for instance, threatening to punish Australia and Canada for their digital platform laws. At the same time its own Attorney General, Pam Bondi crows about a landmark victory “to stop Google from monopolising the digital public square”.