Keegan Payne was fishing in the Northern Territory's Katherine River with one of his sisters and a friend when he hooked the fish on Sunday morning.
The teen was blown away when told he had won the massive prize.
"This is crazy for us. We're a big family, there's eight of us, this is more money than we could ever ask for," Mr Keegan said.
"I can buy what I want, maybe help Dad and Mum out with the home loans."
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The barramundi was released into Top End waters for the ninth season of the annual fishing competition.
Organisers release over a hundred red-tagged fish in Darwin, Katherine, Arnhem Land, Kakadu and Tiwi Islands waterways each year.
Some are worth $1 million and others $10,000.
Season nine has resulted in eight anglers sharing in $80,000 by catching $10,000 fish.
It is the first time in the competition's nine years that the major prize has been won.
Since the competition started in 2015, it has generated more than $70 million in extra spending in the NT and lured more than 10,000 visitors from across the globe to the Top End, providing a significant boost to the tourism industry and businesses.
Charities have also benefited, with sponsor Sportsbet paying $1,000 to the angler's Million Dollar Fish charity partner of choice every time a $10,000 fish is caught.
Mr Keegan's million-dollar barramundi means $10,000 will be donated to the Cancer Council.
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