A local court has ruled that the Dutchman can take his place at Sauber this year, after the Swiss team signed him but then replaced him with Marcus Ericsson and Felipe Nasr.
The ruling is devastating news for Sauber, after the team almost collapsed late last year and only immediate sponsor payments from Ericsson and Nasr kept it afloat.
In Monday's hearing, the team's lawyer said letting van der Garde drive in Melbourne was a safety risk, given that all the testing and car modifications have been made with a different pair of drivers in mind.
But the judge on Wednesday declared that van der Garde's application had been successful due to the law.
"We are disappointed with this decision," said team boss and co-owner Monisha Kaltenborn, "and now need to take time to understand what it means and the impact it will have on the start of our season.
"What we cannot do is jeopardize the safety of our team, or any other driver on the track, by having an unprepared driver in a car that has now been tailored to two other assigned drivers," she added.
29-year-old van der Garde, however, who is backed by his father-in-law Marcel Boekhoorn's McGregor fashion brand, said he is ready to step into the C34 straight away.
"I'm looking forward to going back to the team, work hard and do our best for the weekend," he told reporters in Melbourne on Wednesday.
Van der Garde denied Sauber's claim that he is "unprepared" for Melbourne.
"No, not at all. I'm the fittest ever," he insisted. "I've been training the last three months flat out.
"I'm looking forward to going back to the team. I had a very good relationship – I still have a very good relationship – with the team."
He said he doesn't know if Sauber will vacate Ericsson or Nasr's seat for him.
"Well, I think it's up to them what they're going to do. "It's not my thing," said van der Garde.
He said he would be at the Albert Park circuit later on Wednesday.