The centre-right leader said he wanted the ballot next year on whether to ditch the current flag, which features the Union Jack of former colonial power Britain in one corner.
"I'd like to get on with it, to me I'd like to do it as a 2015 issue," Key told commercial station Radio Live.
"I'm obviously a big supporter of the change, I think there are a lot of strong arguments in favour of the change."
Key has previously said he would prefer a new flag featuring the national plant, a silver fern, on a black background.
Sporting teams such as the All Blacks already use a similar banner and Key argues it is instantly recognisable as a symbol of New Zealand in the same way the maple leaf is a distinctly Canadian icon.
The existing flag was first used in 1869 and formally adopted in 1902. Its supporters say that New Zealanders have fought and died under it for generations and a change would dishonour their memory.
But critics argue it is too easily confused with those of other former British colonies such as Australia, which has an almost identical design.
Key, who increased his share of the vote to convincingly win a third term on Saturday, favours maintaining ties with Britain's monarchy, despite his support for a new flag.
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