Australia has lifted his second Derby in the past three weeks, backing up his Epsom success with a dominant display at the Curragh.
Living up to his billing as a true champion, the regally-bred colt gave trainer Aidan O'Brien his 11th win in the Irish Derby as he trotted up to justify his restrictive odds of 1-8.
Australia's sire Galileo won the Derby in 2001 and his dam, Ouija Board, claimed the 2004 Irish Oaks.
The race was reduced to just five runners with the late withdrawals of Epsom runner-up Kingston Hill and the winner's stablemate, Geoffrey Chaucer.
However, the expectant crowd got the result they had hoped for as Australia completed the Derby double with consummate ease.
Joseph O'Brien made his move on Australia early in the straight before leading a furlong (200m) out and going on to win as he liked.
Eased down close to the post, he was 2-1/2 lengths clear of Kingfisher (25-1) with Orchestra (12-1) third as the Coolmore team filled the first three places.
Aidan O'Brien was delighted with the win.
"It's very unusual that this horse has so much speed," O'Brien said.
"He has so much class that he'd be very comfortable back at a mile (1600m). For him to get a mile and a half the way he does, it's incredible.
"He just relaxes in his races. Pace is his big thing, he just travels.
"I imagine he'll go back to a mile and a quarter now.
"I would say he was made for that race (Irish Champion), and there's also the Juddmonte.
"I'd definitely think about the Arc, but you wouldn't want to run him in bad ground."
Part-owner John Magnier refused to commit to Australia staying in training as a four-year-old.
"It's a relief. It was important for us and exciting for us that he is potentially something you could breed the mares with," Magnier said.
"We knew he was going to be good, it was a matter of how good.
"It's a bit early to talk about that (staying in training as a four-year-old)."