The Hamilton to Auckland train will stop at Frankton, The Base, Huntly, and Papakura (file photo).
It already had support from Waikato Regional, Hamilton City and Waikato District councils, who had been waiting to hear if NZTA would fund $68.4 million so it could go ahead.
"We know more and more people are commuting between Hamilton and Auckland, and introducing this trial service will give them a choice in how they do that," transport minister Phil Twyford said in a statement.
The five-year trial is expected to cost about $78.2m : $68.4m from NZTA and $9.8m from the local councils.
The train would start off with four carriages, allowing it to take 150 passengers each way, Twyford's statement said.
A fifth carriage could be added if needed, increasing the train's capacity to 200 passengers.
"It would stop in Hamilton at Frankton and The Base in Rotokauri before going onto Huntly and finally stopping in Papakura in Auckland, where passengers can change onto the Auckland Public Transport Network," Twyford said.
"Future stops may include Te Kauwhata, Pokeno and Tūākau."
The business case approved by NZTA covers the fit-out of trains and detailed infrastructure design.
Plans are afoot for a Rotokauri rail stop - including a platform and Park & Ride area - and the Huntly platform will need to be upgraded, Twyford said.
Council figures have said doing this and buying the carriages would cost about $49.46m.
The operating costs were within the regional council's Long Term Plan budget while 100 per cent of the capital costs were to be funded by NZTA.
Waikato Regional councillor Hugh Vercoe said in November that if funding was declined, the project would probably be dropped.
Councils are expecting about 20,600 people to want to use the train in the first year, increasing to 103,000 by the third year.
Commuters on the train can expect to pay $12.20 one way to travel 88 minutes from Hamilton to Papakura. Carriages will have wi-fi, a cafeteria, USB power points, toilets and bike racks.
Once passengers reach Papakura, they will need to buy a ticket for the Auckland rail network if they wish to travel on to Britomart.
The service will be contracted to Auckland Transport while ownership of the locomotives pulling the carriages will stay with KiwiRail.
Once the service is running, the Waikato Regional Council wants to explore pushing the service further into Auckland, including the airport.
There would then be a push to swap the diesel engines for electric-run locomotives.
NZTA will now work with local councils and KiwiRail to develop a pre-implementation plan in early 2019.