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 Payne 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.
It is the first time in the competition's nine years that the major prize has been won.
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.
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 Payne's million-dollar barramundi means $10,000 will be donated to the Cancer Council.
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