Former Green MP Sue Bradford will stand for the Mana Party in Waitakere - but will seek the party vote only to increase Labour's chances of taking the seat back from National's Paula Bennett.
Ms Bradford was formally selected by Mana to stand in the seat yesterday.
She said there was a risk she would split the vote on the left, but she intended to make it clear she only wanted the party vote for Mana in the electorate.
Ms Bennett won the seat from Labour's Lynne Pillay by a slim margin of 632 in 2008.
Labour's 2011 candidate, Carmel Sepuloni, said she was not overly concerned Ms Bradford's high profile would create a significant split of the vote on the left, damaging her own chances of winning.