Epic Games, the maker of Fortnite, won a major US court case against Google on Monday, when a jury decided that the search engine giant wields illegal monopoly power through its Android app store.

Epic sued Google and Apple in 2020, accusing the tech titans of abusing control of their respective shops selling apps and other digital content for mobile devices powered by iOS or Android software.

Google and Apple take percentages of all financial transactions at their app shops, prompting complaints by developers about what has been referred to as an unfair "tax" imposed by the companies.

The jury took just a few hours to decide against Google, finding that the company had embarked on various illegal strategies to maintain its app store monopoly on Android phones.

"Victory over Google! After four weeks of detailed court testimony, the California jury found against the Google Play monopoly on all counts," Epic CEO Tim Sweeney said on X (formerly Twitter).

The case now goes back to the judge to decide how to remedy the harm found by the jury.

Google said it would appeal the decision and the case could still drag on for months or years.

"We will continue to defend the Android business model and remain deeply committed to our users, partners, and the broader Android ecosystem," said Wilson White, Google's vice president for government affairs & public policy.

Phones running on the Android operating system have about a 70 percent share of the world's smartphone market.

During the trial it emerged that Google worked aggressively to make sure that the Google Play app store was the only conduit to making payments to third party apps such as Fortnite and other games.

A huge chunk of app store revenue comes from video games and Epic Games has long sought to have payments for its mobile games take place outside the Google or Apple app stores that take a big commission.

Epic had mostly lost its similar case against Apple, where a US judge mostly ruled in favour of the iPhone maker.

Apple and Google regularly argue that their app shop commissions are industry-standard, and that they pay for benefits such as reach, transaction security, and ferreting out malware.

Google is also defending itself in federal court in Washington, where Justice Department officials accuse the company of acting illegally to preserve the dominance of its world-leading search engine.

At the heart of the case by the department is Google's massive revenue sharing deals in which iPhone maker Apple takes a big cut of Google ad revenue made from being the default search engine on Apple devices. (AFP)