New Zealand adopted the German-style Mixed Member Proportional (MMP) system in 1996 after an inquiry found smaller parties were being shut out of parliament under the previous first-past-the-post system adopted from Britain.
Luxon said in an interview with radio station Newstalk ZB that a referendum is "something we should consider", and could be held as early as 2027 if he returns to power following a general election scheduled for November 7.
"I think I would because I actually think that it is quite right to check in constitutionally and say, is this the system, New Zealand, you still want?" he said.
Under MMP, constituents cast two votes: one for a local candidate and one for a party.
Winning local candidates in 71 constituencies take their seats automatically, while the remaining seats are filled from party lists, allocated to match each party's share of the nationwide vote.
There are expected to be around 49 list seats in the upcoming election, though that number may vary due to the quirks of the system.
MMP has been praised for allowing smaller parties a say in government, but criticised for its complexity and for often requiring coalition governments.
It also has several unusual features, including seven seats reserved exclusively for Indigenous Maori voters.
New Zealand's general election will be held on November 7.
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