The $30 billion expansion project, for an open-pit cooper, uranium and gold mine, has the potential to boost production from about 180,000 tons a year to 750,000 tons a year for decades, BHP says.
Olympic is the world's fourth-largest copper and gold deposit and the largest known uranium deposit.
BHP has said the expansion would create more than 13,000 jobs and contribute more than $45 billion to South Australia's economy over the next 30 years.
Overall mining currently brings $80 billion a year of gross value added into Australia's economy, says the federal government.
The expansion would include building an airport, a gas-fired station, a 65-mile rail line and a coastal desalination plant.
BHP Billiton Uranium President, Dean Dalla Valle called the approval "the culmination of one of the most comprehensive and rigorous environmental assessment processes undertaken in Australia and is another important milestone as we seek to develop this world class ore-body."
The approval, under federal environmental law, calls for the mining giant to "adhere to more than 100 stringent conditions" including establishing a biodiversity conservation area of 346,000 acres.
"My decision is based on a thorough and rigorous assessment of the proposed Olympic Dam mine expansion including independent expert reviews and consideration of public comments received on the project's environmental impact statement," Environment Minister Tony Burke said.
But Australian green groups maintain that the mine expansion would severely expose South Australia to radioactive waste and use massive amounts of water.
The project would create a "carcinogenic mountain range," because tailings, the waste from the uranium extraction and processing, would remain on the surface instead of being buried in a lined pit, said Sen. Scott Ludlam, the Greens' spokesman on nuclear issues.
''That isn't a radioactive waste heap -- that's a radioactive waste mountain range. The so-called environment conditions are hopeless -- there's no requirement for this tailing heap to be covered while the mine operates," he was quoted as saying in Tuesday's edition of The Sydney Morning Herald.
The expansion also means that the mine's requirement for water will increase from 11 million gallons a day to an average of 63.4 million gallons a day.
The BHP Billiton Board is expected to make a decision on the expansion next year. The company will need to obtain a new operating license from the South Australian government for the project.