[3] It is now owned by the Bay of Islands Vintage Railway but regular operations were suspended in 2001, with resumption on a short section of the line in 2008.

Eventually, it became clear that a mainline was required to link these isolated railways to improve transport for both passengers and freight to and from New Zealand's northernmost region, and to open up land for greater economic development.

It was constructed not as a railway, but as a wooden-railed bush tramway to carry coal to the wharf for export, and was built to the international standard gauge of 4 ft 8+1⁄2 in (1,435 mm).

The local member of parliament announced the construction of a tramway on 7 August 1889, but both that year and next, the Public Works Department (PWD) rebuffed him.

In 1891, Whangarei interests established a syndicate to extend the line under the Railways Construction and Land Act of 1881,[18] and their detailed offer prompted the newly elected government.

The Railway Authorisation and Management Act of 1891 [19] approved the extension by transferring funds from a plan to duplicate the line from central Auckland to Penrose.

Locals believed this was the first part of the link to Kawakawa, but Richard Seddon had not authorised the full project, just the extension to the Puhipuhi forest.

This was originally meant to terminate in Whakapara, but a further extension to Waiotu was required to provide easier access and this opened on 28 December 1898.

However, a lack of detailed surveys, poor finances, unstable terrain, and the PWD being overburdened with jobs contributed to a slow rate of progress.

[23] The former became the site of a small locomotive depot, while the latter was established as the northernmost terminus for passengers until the full line was finished.

Work thus proceeded from both ends to link Huarau and Portland via Waiotira, though this was not without dispute as local interests clamoured for alternate routes.

The PWD was able to offer a freight service between Huarau and Portland from 1923, but some parts of the line were only temporary due to difficulties with the terrain.

The floor of the tunnel was excavated to a new level, and then the rails, sleepers and ballast were relaid; the work commenced in February 1968 and was completed in November.

These popular services barely lasted longer than a decade, being withdrawn in July 1967 as the railcars proved mechanically unreliable.

The Auckland Harbour Bridge had opened in 1959 and drastically cut road transport times north, and in the face of heightened competition, the railway could not compete.

Passenger carriages were now attached to some freight trains to create mixed services that ran between Whangārei and Auckland and from Whangārei to Ōkaihau and Opua; as they adhered to the freight schedules, the mixed trains ran much slower than the previous dedicated passenger services.

[33] Freight carriage in the North tended to suffer from thin settlement and heavy competition from New Zealand's coastal shipping.

By 2019, only one weekday return freight service operated on the line, largely carrying dairy and timber products.

[38] In 2007, an upgrade of the North Auckland Line was described by Northland Regional Council chairman Mark Farnsworth as an important stage in the construction of the Marsden Point Branch.

The upgrade would increase tunnel clearances to enable large freight containers to be conveyed between Marsden Point and Auckland.

[40] In 2014, KiwiRail decided not to upgrade the line to meet national standards of clearances and wagon axle-loads due to a lack of finance.

[47] The business case found the total cost of the upgrade and new branch line to Marsden Point would be NZ$1.3 billion, with a benefit-cost ratio of 1.19 (assuming NorthPort's expansion goes ahead), meaning for every $1.00 spent there would be a return of $1.19.

[48] [47] The report said that speed restrictions and length made the line impractical for commuter passenger travel and some types of freight.

[50] On 6 September 2019, the Regional Development Minister Shane Jones announced at Helensville railway station a grant of $94.8 million for upgrades on the 181 km line, without which it could have been closed within a year according to KiwiRail.

[51] The work includes replacing five ageing wooden bridges of the 88 bridges on the line with concrete bridges ($16.2M); repairing 13 tunnels ($7.3M) including steel support ribs in No 2, Makarau and investigating ground conditions for later track lowering; upgrading or replacing about 54 km (30%) of track sleepers and ballast with 50,000 sleepers and 50,000 cubic metres of ballast ($53.1M); clearing drains and replacing about 237 (25%) of the 950 culverts ($9.5M); stabilising nine embankment slopes ($4.7M); vegetation control ($0.8M) and improving Whangarei Rail Yard ($3.2M).

[53][54] KiwiRail had expected the rejuvenation work to be largely complete by September 2020, cutting 1½ hours off the 2019 schedule, and that trains could be running to Marsden Point by 2023.

[55] A business case for building the Marsden Point rail link is under development it estimated to take five years to build once approved[50] In 2023 Cyclone Gabrielle undermined part of the line and caused a 60,000 m3 (78,000 cu yd),[56] or 35,000 m3 (46,000 cu yd), slip onto the line and a minor road, just south of Tahekeroa tunnel, as well as about 50 other slips between Swanson and Whangārei.

The line reopened on 26 September 2024 [57] When the railway around Whangārei was isolated from the national network, it was home to up to half of the members of the WB class.

In 1968, the Makarau tunnel (573m) north of Helensville was made larger to accommodate the DA class and they were the dominant motive power well into the 1980s.

The Linesider magazine stated in its December 2022 edition that DL operation on the North Auckland Line is "likely to begin later this year.