The benchmark S&P/ASX200 index was up 58 points, or 0.7 per cent, to 8,310.8 at noon AEDT on Tuesday - its first time ever above 8,300.
The broader All Ordinaries was up 55.4 points, or 0.65 per cent, to 8,584.1.
The gains came after a strong lead from Wall Street, where the Dow Jones and S&P 500 hit another record high.
"While a clear catalyst for last night's rally was absent, the fundamental narrative is the same: the US economy is on solid footing, easier monetary policy and loose fiscal settings are waiting for market participants in 2024, and world-beating productivity is making it all possible by keeping inflation relatively contained," Capital.com analyst Kyle Rodda said.
Eight of the ASX's 11 sectors were higher at midday, with energy and utilities lower and consumer staples basically flat.
The heavyweight financial sector was the biggest gainer, rising 1.3 per cent as Westpac and CBA both climbed 1.7 per cent, NAB added 1.5 per cent and ANZ gained 0.9 per cent.
In the heavyweight mining sector, BHP was up 1.1 per cent, Fortescue had added 2.3 per cent and Rio Tinto had advanced 1.6 per cent.
The energy sector was lower after Brent crude slumped to a 12-day low of $US75 a barrel following bearish economic data out of China.
Woodside was 1.6 per cent lower, Santos had dropped 1.3 per cent and Whitehaven Coal had dropped two per cent.
The Australian dollar was buying 67.32 US cents, from 67.41 US cents at Monday's ASX close.