Former cabinet minister Damien O'Connor was today formally declared elected to Parliament.
He has replaced Michael Cullen, who retired earlier this week.
Dr Cullen was a list MP, which meant there did not have to be a by-election to replace him.
Mr O'Connor, who lost the West Coast-Tasman seat to National's Chris Auchinvole in last year's general election, was the next on Labour's list.
The Chief Electoral Office issued notification of Mr O'Connor's election.