In a video released by NSW Health, Mr O'Brien was overwhelmed with emotion as he said a heartfelt thank you to his 'blue angels'.
He said: 'They gave me my life back. There's no words I can use to express myself.
'This is the best hospital in the world, the best people in the world, the best medical staff in the world
'I'm the proof. I'm the miracle man.'
Mr O'Brien said he was in and out of consciousness for much of his treatment after contracting Covid-19.
But he credits his many years as a singer for his healthy lungs and believes this helped his survival.
He has urged other Aussies to stay home as much as they can while the country continues to flatten the curve.
'Don't overdo it, just think of your fellow neighbours,' he said.
NSW recorded 12 new cases of coronavirus overnight and the country's death toll has risen to 88.
But authorities say the rate of community transmission remains low, with many states beginning to roll back lockdown restrictions.