The Hamilton West byelection date has been set after former Labour MP Gaurav Sharma this week announced his resignation.
Prime Minister Jacinda Ardern said the byelection would be held on Saturday, December 10 this year.
Sharma resigned from Parliament earlier this week, forcing a byelection in the Hamilton West electorate.
Sharma was expelled from the Labour caucus in August after going rogue and making claims about bullying within the party, which Labour has denied after conducting an internal investigation.
The party was also deciding whether to expel Sharma as a Labour Party member.
In a social media post on Tuesday, Sharma detailed the process undertaken by the party over recent weeks, much to the disappointment of the party that enforced confidentiality requirements on such proceedings.
Sharma's central claim alleged NZ Council members informed him the party planned to invoke waka-jumping legislation to kick him out of the party, but not until six months out from next year's general election so as not to trigger a byelection, which traditionally costs taxpayers about $1 million.
Fearing this would leave Hamilton West constituents without a voice in Parliament for six months, Sharma resigned on Tuesday, confirming a byelection would take place.