Work would begin on the Carmichael coal project in Queensland state's Galilee Basin and on a 400-kilometer (250-mile) rail link to an expanded port on the coast in June or July, Adani's Australian chief executive Jeyakumar Janakaraj said.
"We want to start construction in the middle of next year," he told reporters.
Environmentalists are concerned that the 22 billion Australian dollar ($16 billion) project will damage the nearby Great Barrier Reef.
Indian resource billionaire Gautam Adani's corporation has most of the government approvals needed to proceed with the project that has been planned for six years and fought by environmentalists in the courts.
But the investment decision is not yet final and the company is seeking a cheap loan from the Australian government to build the rail infrastructure.
Adani announced Tuesday that the project's regional headquarters would be the north Queensland city of Townsville.
Queensland Premier Annastacia Palaszczuk said the project would create 10,000 jobs in a region that has economically suffered in recent from a mining downturn.