Witnesses saw the koala survive being hit by a car before retreating into treetops where it passed out from its injuries.
Rescuers from Wildlife Victoria had to toss the animal's dying body from the tree into a safety net before massaging the area around its heart and administering mouth-to-mouth.
"This isn't something we'd do all of the time but it shows the dedication of volunteers to saving wildlife," Amy Amato, a spokeswoman for Wildlife Victoria, told the Guardian.
"He is currently being rehabilitated in a wildlife shelter and will be assessed by a vet today. Fingers crossed, with the right care he'll be OK. Often we get koalas when it's too late, but he seemed to be in fairly good shape. He might just need some R&R."
Although originally thought to be well-known local marsupial Sir Chompsalot, the koala was an unknown animal resident of the area and has been named "Sean."