The 6-3 decision centres on tariffs imposed under an emergency powers law, including the sweeping "reciprocal" tariffs he levied on nearly every other country.
It's the first major piece of Trump's broad agenda to come squarely before the nation's highest court, which he helped shape with the appointments of three conservative jurists in his first term.
The majority found that the constitution "very clearly" gives Congress the power to impose taxes, which include tariffs.
"The Framers did not vest any part of the taxing power in the Executive Branch," Chief Justice John Roberts wrote.
Justices Samuel Alito, Clarence Thomas and Brett Kavanaugh dissented.
"The tariffs at issue here may or may not be wise policy. But as a matter of text, history, and precedent, they are clearly lawful," Kavanaugh wrote in the dissent.
The majority did not address whether companies could get refunded for the billions they have collectively paid in tariffs.
Many companies, including the big-box warehouse chain Costco, have already lined up for refunds in court, and Kavanaugh noted the process could be complicated.
"The court says nothing today about whether, and if so how, the government should go about returning the billions of dollars that it has collected from importers. But that process is likely to be a 'mess,' as was acknowledged at oral argument," he wrote.
The Republican president has been vocal about the case, calling it one of the most important in US history and saying a ruling against him would be an economic body blow to the country.
But legal opposition crossed the political spectrum, including libertarian and pro-business groups that are typically aligned with the Republican Party.
Polling has found tariffs aren't broadly popular with the public, amid wider voter concern about affordability.
The Supreme Court ruling comes despite a series of short-term wins on the court's emergency docket that have allowed Trump to push ahead with extraordinary flexes of executive power on issues ranging from high-profile firings to major federal funding cuts.
The tariff decision doesn't stop Trump from imposing duties under other laws.
While those have more limitations on the speed and severity of Trump's actions, top administration officials have said they expect to keep the tariff framework in place under other authorities.
The Constitution gives Congress the power to levy tariffs.
But the Trump administration argued that a 1977 law allowing the president to regulate importation during emergencies also allows him to set tariffs.
Other presidents have used the law dozens of times, often to impose sanctions, but Trump was the first president to invoke it for import taxes.
Trump set what he called "reciprocal" tariffs on most countries in April 2025 to address trade deficits that he declared a national emergency.
Those came after he imposed duties on Canada, China and Mexico, ostensibly to address a drug trafficking emergency.
A series of lawsuits followed, including a case from a dozen largely Democratic-leaning states and others from small businesses selling everything from plumbing supplies to educational toys to women's cycling apparel.
The challengers argued the emergency powers law doesn't even mention tariffs and Trump's use of it fails several legal tests, including one that doomed then-President Joe Biden's $US500 billion ($A711 billion) student loan forgiveness program.
The economic impact of Trump's tariffs has been estimated at some $US3 ($A4.3) trillion over the next decade, according to the Congressional Budget Office.
The Treasury has collected more than $US133 billion ($A189 billion) from the import taxes the president has imposed under the emergency powers law, federal data from December shows.
The European Union is carefully analysing the decision by the US Supreme Court to strike down Trump's sweeping tariffs.
"We remain in close contact with the US Administration as we seek clarity on the steps they intend to take in response to this ruling," the EU spokesperson said.
"Businesses on both sides of the Atlantic depend on stability and predictability in the trading relationship. We therefore continue to advocate for low tariffs and to work towards reducing them."
with Reuters
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