Peter Dunne is standing down after 33 years as Ōhāriu’s MP.
Dunne has said he is retiring due to a “mood for change” in his electorate.
A recent poll showed Labour candidate Greg O’Connor 14 points ahead of Dunne.
Mr Dunne’s is the leader of the United Future party. The United Future Party – alongside ACT and the Māori Party – has been a support partner of National.
His announcement today follows a change in leadership for Labour, with Andrew Little stepping down in favour of Jacinda Ardern on 1 August, and Metiria Turei’s resignation as Green Party co-leader eight days later.