The line featured in Julius Vogel's 1870 Great Public Works programme and construction resumed in 1872, to New Zealand's new narrow gauge of 3 ft 6 in (1,067 mm).

In 1903, electric trams were introduced between Auckland and Onehunga, running along Manukau Road, resulting in a significant drop in passenger patronage on the branch line.

Also, Auckland and Wellington were directly connected by rail with the first scheduled services in February 1909 on the North Island Main Trunk line.

Freight shunts continued to operate as far as Mays Rd until late 2007 and an annual enthusiasts excursion with ADL class DMU ran until 2006.

The last steam trains before closure was a series of excursions over Labour Weekend 1993 with a tank engine and carriages from Glenbrook Vintage Railway.

JA 1275 ran shuttle trains with DC 4536 on 18 September 2010 to celebrate the reopening of the line, before regular passenger services commenced the next day.

[10] The petition was presented to the ARC, which formally endorsed it and passed it to its subsidiary, ARTA, recommending that passenger services should be started to both Onehunga and to Helensville.

[11] In August 2007, coastal shipping firm Pacifica Shipping called for the section of the line between Onehunga Wharf and the end of the line at the Port of Onehunga to be reopened,[12] to allow for export freight from the South Island to be unloaded at the wharf and transferred by rail to the Ports of Auckland on the Waitematā Harbour.

[citation needed] In mid-2010, construction started on the terminal station at Onehunga, and its opening was delayed past its intended date to September 2010.

The ARC also used $8 million to buy the site for the Onehunga station, where a 60-space park and ride facility was to open one week after the train services began.

In early 2007, NZTA's predecessor Transit New Zealand announced that a project to double the width of the Māngere Bridge across the harbour would accommodate a rail link.

[22] The duplicate bridge was built to accommodate the link, and NZTA has provided for a rail corridor near the motorway as far as Walmsley Road.