Phil Goff was confirmed as New Zealand's new Labor Party leader to replace Helen Clark, who stepped down following the party's defeat in Saturday's general elections.
The unanimous decision was announced on Tuesday following a meeting of the Labor caucus.
Annette King was elected as deputy leader while David Cunliffe will be finance spokesman.
Outgoing Prime Minister Helen Clark was named as foreign affairs spokeswoman.
Goff said Labor would be a strong and effective Opposition.
"In Government Labor succeeded because it had a united, disciplined and motivated parliamentary and ministerial team," Goff told a press conference.
"The outcome of today's caucus demonstrates that Labour will be a strong, united and determined Opposition," he added.
Michael Cullen will be Shadow Leader of the House. Darren Hughes and Steve Chadwick would be senior and junior opposition whips respectively.
Clark spoke in public on Tuesday 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.
Phil Goff, 55, holds the seat of Mt Roskill in Auckland. He first entered the Parliament in 1981, was defeated in 1990 and re-elected in 1993.
He held the Defence, Trade, Corrections and Associate Finance portfolios in the last term. He ranked fourth in the cabinet.
He says the Labour Party was defeated in the election because the public wanted change, but that Labour still has a lot to offer.
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. King is ranked fifth in the cabinet.