New York federal court applies broad preclusive effect and adopts DOJ’s Google ad tech ruling

The United States District Court for the Southern District of New York recently ruled, in favor of publishers and advertisers, that Google monopolized worldwide markets for publisher ad servers and ad exchanges and unlawfully tied its ad server to its ad exchange in violation of Sections 1 and 2 of the Sherman Act.

US District Judge P. Kevin Castel’s partial summary judgment ruling, filed on October 27, 2025, narrows the scope of the ongoing multidistrict litigation (MDL) concerning Google’s digital advertising practices.

Judge Castel’s opinion applied principles of issue preclusion and based the decision upon an April 2025 bench trial ruling from the US District Court for the Eastern District of Virginia, which found Google liable for similar claims brought by the US Department of Justice (DOJ) and 17 states.

The MDL ruling underscores the potential for plaintiff-side offensive issue preclusion in parallel private litigation due to DOJ antitrust enforcement actions.

The DOJ decision provides the basis for preclusion.

The MDL consolidates several federal actions against Google and related entities, brought by publishers, advertisers, and other private parties, all alleging anticompetitive conduct in Google’s digital advertising business.

Among other claims, the MDL plaintiffs allege that Google willfully engaged in a series of anticompetitive acts to acquire and maintain monopoly power in the publisher ad server and ad exchange markets and unlawfully tied its publisher ad server and ad exchange, violating Sections 1 and 2 of the Sherman Act.

In the parallel bench trial in the Eastern District of Virginia, US District Judge Leonie M. Brinkema found Google liable for monopolization of the publisher ad server and ad exchange markets and for unlawful tying of its publisher ad server and ad exchange “through contractual policies and technological integration, which enabled the company to establish and protect its market power in these two markets.”

Given the substantial overlap between the DOJ action in Virginia and the MDL, plaintiffs in the MDL sought partial summary judgment, arguing that Google should be precluded from relitigating issues already decided in the DOJ action.

The MDL meets the standard for issue preclusion.

In granting partial summary judgment for plaintiffs in the MDL, the Southern District of New York (the MDL court) determined that the circumstances met all the principles of issue preclusion.

Issues litigated in the DOJ action were, as Google itself had characterized them in other filings, “substantively identical” to those raised by the MDL plaintiffs. The MDL court ruled that Google had a robust opportunity to defend itself in the DOJ action, which involved extensive discovery and a lengthy bench trial during Google’s defense of the MDL action.

The MDL court explained that the fact that the DOJ action was a bench trial was crucial to the issue preclusion finding because, while a jury trial may leave an open question as to “which type of anticompetitive conduct the jury actually and necessarily found as a predicate for its ultimate finding of monopolization,” the bench trial allowed the court in the DOJ action to make specific findings necessary to its judgment.

The MDL court also concluded that procedural differences between the cases raised by Google were immaterial, as well as Google’s contention that differences in legal standards between the US Courts of Appeals for the Second and Fourth Circuits barred the use of issue preclusion. The court found no unfairness in applying issue preclusion, reasoning that preclusion would promote judicial efficiency without causing jury confusion.

The decision may implicate more than the MDL.

This decision highlights the downstream impact of government antitrust decisions. Courts may consider granting plaintiff-side offensive issue preclusion where facts and theories overlap, even before a final judgment on remedies.

In future parallel enforcement and private actions, parties litigating in this arena may see an increased emphasis on cross case coordination and consistent market definitions.

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