The superstar came onstage for the special gig Down Under almost an hour late on Wednesday night (July 13), totally befitting her pop diva status.
But she instantly got the 1,000-strong Aussie audience on side, telling them: 'I'm so happy to be in Australia, I won't leave it so long the next time before I get to come back again.'
She played all her hits, including Telephone, Born this Way, Alejandro, Poker Face and Bad Romance.
Fans who attended had all won competitions to see the gig.
Many had dressed up, Gaga-style for the occasion.
The organ, the largest pipe organ in the world, was installed in 1890.
The Town Hall was Sydney’s premier music venue before the Opera House opened in 1973.
It was renamed the 'Monster Hall' for Lady Gaga's gig, in honour of her fans.