The ruling provided an extra shot in the arm for investors already upbeat after forecast-busting earnings from chip titan Nvidia revived optimism about the tech sector.
And while the White House has appealed against the decision, analysts said traders were making the most of the buying opportunity on hopes the levies will not be imposed.
After hearing cases brought by businesses and a coalition of state governments, the three-judge Court of International Trade agreed that the president's actions violated the power of the purse given to Congress under the constitution.
The White House slammed the ruling by "unelected judges".
The news revived risk appetite among investors, who remain anxious despite slowly recovering from the shellshock of the president's April 2 "Liberation Day" tariffs that fanned fears of a global recession.
Markets in Japan and South Korea -- major exporters who faced huge tariffs -- surged more than one percent thanks to rallies in tech firms and auto makers.
Seoul was also helped by a central bank interest rate cut.
Hong Kong, Shanghai, Sydney, Taipei and Manila were also higher, while the futures for all three main indexes in New York piled on more than one percent each.
- 'Market exhaling' -
The gains were helped by a rally in tech firms that came after Nvidia reported better-than-expected first-quarter earnings, even as it faced increased export controls that it warned could cost it billions in the current quarter.
The firm posted a profit of $18.8 billion on revenue of $44.1 billion, and forecast strong sales for the second quarter, thanks to still-booming demand for chips to power artificial intelligence.
Stephen Innes at SPI Asset Management said investors extending the Nvidia-fuelled rally showed "the market exhaling after weeks of white-knuckle volatility sparked by trade war brinkmanship," he wrote in a commentary.
US judges gave a clear message, Innes said: "The Oval Office isn't a trading desk, and the Constitution isn't a blank cheque."
The ruling is "a structural pivot in the narrative: from strongman tariffs to institutional guardrails", he said.
"Executive overreach may finally have found its ceiling. And with it, a fresh dose of macro stability -- at least until the next headline."
The prospect that the worst of the tariffs could be avoided also weighed on safe-haven assets, with gold and the yen retreating.
Oil, meanwhile, extended Wednesday's rally that was already underway ahead of an OPEC meeting to discuss output and rising tensions over Russia and Iran.
- Key figures at around 0230 GMT -
Tokyo - Nikkei 225: UP 1.7 percent at 38,355.70 (break)
Hong Kong - Hang Seng Index: UP 0.4 percent at 23,347.38
Shanghai - Composite: UP 0.6 percent at 3,359.32
Euro/dollar: DOWN at $1.1242 from $1.1291 on Wednesday
Pound/dollar: DOWN at $1.3430 from $1.3468
Dollar/yen: UP at 145.89 yen from 144.82 yen
Euro/pound: DOWN at 83.71 pence from 83.84 pence
West Texas Intermediate: UP 1.1 percent at $62.50 per barrel
Brent North Sea Crude: UP 1.0 percent at $65.54 per barrel
New York - S&P 500: DOWN 0.6 percent at 5,888.55 (close)
London - FTSE 100: DOWN 0.6 percent at 8,726.01 (close)
dan/rsc
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