Glencore Xstrata had already received federal clearance to expand the mine, but has been awaiting final approval from the Northern Territory Government.
Northern Territory Mines and Energy Minister Willem Westra van Holthe said the Mining Management Plan for the McArthur River Mine phase three development project has been approved and the planned expansion would be worth $369m and create 300 new jobs.
MRM, which holds the world's largest zinc-lead deposits, is located 900km south-east of Darwin in the Gulf region.
The Mining Management Plan for the McArthur River Mine phase three development project would extend the life of the mine by nine years to 2036.
"MRM and their parent company Glencore Xstrata have committed to spending 75% of capital expenditure and 100% of operational expenditure for the project with Northern Territory suppliers and industry.
"Over the life of the mine, this expansion will boost industry output by $8.4bn within the Northern Territory economy," Holthe added.
Xstrata, which merged with Glencore last month, gained control of McArthur River mine in 2003 when it acquired Mount Isa Mines mine.
The planned expansion of MRM comes almost a month after the merged entity announced that it would drop the plans to build a coal export terminal in Queensland.
Image: McArthur River Mine, located in the Northern Territory outback, holds the world's largest zinc-lead deposits.