The S&P/ASX200 spiked by 0.37 per cent in early trade but was 0.15 per cent, or 12.3 points higher by midday, to 8,4109.2.
The broader All Ordinaries gained 12.2 points, or 0.14 per cent, to 8,637.1.
Wall Street edged lower overnight, but S&P500 futures have rallied in after hours trading on the back of chip designer Nvidia's strong earnings.
"The company posted another strong quarter ... with revenue reaching US$44.1 billion ($A68.8 billion) bringing year-on-year growth to 69 per cent," VanEck cross asset research specialist Anna Wu said.
The US dollar rallied against major currencies after the New York-based Court of International Trade blocked President Trump's Liberation Day tariffs from taking effect.
The court found the president overstepped his authority in invoking emergency legislation to level the tariffs, and only Congress had authority to regulate US trade.
"This ruling reaffirms that our laws matter, and that trade decisions can't be made on the president's whim," Oregon Attorney General Dan Rayfield said in a statement.
The White House is appealing the decision.
Seven of 11 local sectors were trading higher by midday, but real estate (-0.4 per cent) and materials (-0.2 per cent) weighed on the bourse.
Energy was leading the gains, up 1.7 per cent as oil prices spiked more than 1.5 per cent on the tariff decision, and as the US mulls more sanctions on Russia over the war in Ukraine.
Brent crude futures were trading at $65.02 a barrel, as their West Texas equivalent rose to $US62.03.
Financials stocks eked out a 0.2 per cent gain, with the big four banks mixed as Westpac lifted 0.5 per cent and ANZ fell 0.3 per cent.
The Commonwealth Bank was down 0.1 per cent to $173.65 after hitting a new record above $176.50 last week.
Local IT stocks took their lead from the US tech sector, up 0.7 per cent as Megaport (+2.7 per cent) and NextDC (+1.1 per cent) pushed higher.
The materials sector lost 0.2 per cent, with large cap miners BHP (-0.3 per cent) and Rio Tinto (-0.7 per cent) down as iron ore price weakness remained stubborn.
The Australian dollar is buying 64.20 US cents, down from 64.31 US cents on Wednesday at 5pm but it's higher against most major currencies.
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