"This is a significant and welcome contribution to supporting population and economic growth in the Hamilton to Auckland corridor, and it's an example of partnerships and collaboration producing great results," Mr King said.
Labour MP Jamie Strange, who is based in Hamilton, said the rail service is an important step towards a more diverse transport system.
"The Waikato expressway and the commuter rail will work in tandem, giving people options around their transport needs," Mr Strange said.
"A key benefit will be productivity: People will be able to board the train, open their laptop and start working.
"This was very much a team effort, but I would like to acknowledge the advocacy of councillor Dave Macpherson and former Labour MP Sue Moroney over the last few years."
The service would start in Hamilton at Frankton then go to The Base in Rotokauri before going on to Huntly and stopping in Papakura in Auckland, where Auckland passengers change to the city's electric trains to travel to Britomart and stops along the way.
It will run twice a day, leaving at around 5am and 7am, costing passengers $40 for a round trip.
A new station including a platform and Park & Ride area will be created as part of the Rotokauri rail stop, while the existing Huntly platform will be upgraded.
The service would start with a four-carriage train which can carry 150 passengers each way.
As demand grows, it is expected to be expanded to a five-carriage train carrying up to 200 passengers.