The Finance and Transport ministers have signed an agreement with Auckland mayor Phil Goff to create a new entity in charge of finishing the City Rail Link.
City Rail Link Limited (CRLL), a company jointly owned by central and local government, is now responsible for the project, which is estimated to cost between $2.8 billion and $3.4 billion.
Retired NZ Post boss Sir Brian Roche will chair the company.
Transport Minister Simon Bridges said the CRL was Auckland's top transport priority.
"It will double the capacity of the whole existing rail network and provide significant travel time savings for commuters.