Labour MP Sue Moroney will retire from Parliament at this year's election.
She said she made the decision after she was not ranked high enough on the party list.
Ms Moroney has been an MP since 2005 and was the party's chief whip while David Cunliffe was leader in 2013 and 2014.
She is based in Hamilton but has never held an electorate seat.
She promoted a bill to extend paid parental leave.
Labour leader Andrew Little said he understood her reasons for standing down and that her contribution to the Labour caucus would be missed.