Dunedin South MP David Benson-Pope has confirmed he will not be standing for re-election in November.
Mr Benson-Pope resigned from his position as Environment Minister last year, and subsequently lost the Labour Party's nomination for Dunedin South to Clare Curran.
Mr Benson-Pope said on Monday his decision was made after long and difficult consideration.
He said he could not allow a personal sense of betrayal to stand in the way of his political philosophy and urged votes to give their party vote to Labour.
In 2007, Prime Minister Helen Clark said Mr Benson-Pope had misled the public over what he knew about the dismissal of an Environment Ministry staff member, which prompted Mr Benson-Pope's resignation.