Phil Goff has been confirmed as the new Labour leader to replace Helen Clark.
The unanimous decision was announced at a press conference at the Beehive this afternoon following a meeting of the Labour caucus.
Annette King has been elected as deputy leader while David Cunliffe will be finance spokesman.
Outgoing Prime Minister Helen Clark has been named as foreign affairs spokeswoman.
Mr Goff said Labour would be a strong and effective Opposition.
"In Government Labour succeeded because it had a united, disciplined and motivated parliamentary and ministerial team," Mr Goff said.
"The outcome of today's caucus demonstrates that Labour will be a strong, united and determined Opposition."
He said Labour's 13 new MPs gave it new experience and fresh talent.
Michael Cullen will be Shadow Leader of the House. Darren Hughes and Steve Chadwick would be senior and junior opposition whips respectively.
Helen Clark spoke in public today for the first time since her resignation speech on Saturday night. She said she was confident she had made the right decision for the party and herself.
She also pledged to give "complete and unconditional" support to the new leader.
Earlier today, senior Labour MP Chris Carter told journalists that Labour was a "united" and "decisive" party.
"I think we will find Phil Goff to be the leader today," Mr Carter said.
Mr Carter praised Mr Goff for his energy and hard work, and indicated Mr Goff would be elected unopposed.
Helen Clark announced she was standing down after Saturday night's election result.
So did her deputy, Dr Cullen, and the caucus had to replace him as well.
Several MPs, including Ruth Dyson and Shane Jones, had been mentioned as possible contenders for the deputy leadership. Another contender Maryan Street ruled herself out.
Labour was known to want a man and a woman in the top two positions, believing that would be the most effective way to take on National's John Key and his deputy Bill English.
Mr Goff was a minister in the Labour government that was in power from 1984 to 1990, and from 1999 to the present.
He was foreign minister from 1999 to 2005, when the position was given to Winston Peters as part of its support deal with Labour.
Mr Goff took on defence, trade and corrections. He is ranked fourth in the cabinet.
Ms King also has wide experience as a minister.
She held the employment and immigration portfolios in the previous Labour government and was minister of health from 1999 to 2005. Since then she has held the justice, police and transport portfolios. Ms King is ranked fifth in the cabinet.