The 23-year-old was able to talk to friends at ringside in the moments after a points defeat in his home town of Toowoomba, but he later collapsed and was taken to hospital in Brisbane.
Doctors placed Smith an an induced coma, and family spokesman James O’Shea announced his death on Monday.
Nicknamed ‘The Great White’, featherweight Smith was unbeaten in 12 fights before Saturday and was combining his boxing career with studying for a law degree.
O’Shea, quoted by the Australian Associated Press, said: “He really wanted to change the image of boxing. A lot of times in this country the sport gets a bad rap. A big goal of his life was to show people it’s not (a bad sport).”