The 49-year-old former Wham! front man tweeted Tuesday "Hey everyone, it's that time again! And I get to open the tour singing to the men and women who saved my life."
Austrian media says 300 medical personnel from the hospital where Michael was treated are attending the concert Tuesday.
Michael was in the middle of his "Symphonica" tour when he fell ill in Vienna in November. He spent several weeks in the hospital and later said his survival had been "touch and go."
A second Vienna concert is planned for Thursday.