In 1866, the government's investigating committee approved the line and the Wellington, Hutt Valley and Wairarapa Railway Ordinance [2] was passed on 2 July 1866.

Steam locomotives had now arrived to work the line and service began, with four trains daily each way (three on Sundays).

The Pipitea Point railway station terminus in Wellington was destroyed by fire on 16 January 1878, but remained open.

On 25 May 1927 signalling and interlocking on the double track Hutt Valley Junction to Waterloo (then a branch) was introduced.

a switch-lock trailing crossover named Halfway was installed between Ngahuranga and Petone at Rocky Point, to allow single-line working when the seaward side (south) track was unusable because of southerly storms.

[13] Construction was simple with minimal earthworks, although industrial troubles in Britain delayed delivery of steel girders, and the temporary structure was nearly washed away by a flood.

[8] In 1938, the Minister of Railways Dan Sullivan said that the extension and duplication of the line from Waterloo to Silverstream or Upper Hutt had not yet been considered by Cabinet.

The following day, the new Taitā to Haywards section opened and the Hutt Valley Branch was incorporated into the Wairarapa Line.

[17][18] Electrification had been approved in response to post-WWII coal shortages and was also implemented in the 1950s, with the first electrified section opened on 14 September 1953 from the North Island Main Trunk junction at Kaiwharawhara to Taitā.

[17] On 19 July 1954, the railway was duplicated to a point north of Haywards, and on 21 November a single track on the new Silverstream deviation was brought into use.

[19] On 24 July the electrification was completed to Upper Hutt and diesel-hauled suburban passenger trains north of Taitā ceased.

In November 2013, the Greater Wellington Regional Council (GWRC) voted to close it permanently as on health and safety grounds, it was too expensive and nearly impossible to upgrade the station to provide step free access via ramps for disabled passengers.

Initially projected to take eighteen months and to cost $300 million, the upgrading was completed (after two years) with the first trains running on 14 November 2021.

The substations are located at Wellington, Kaiwharawhara, Petone, Woburn, Pomare, Silverstream, and Upper Hutt.

Also along the line are three "cross-tie" substations at Rocky Point, Epuni, and Heretaunga, which provide a switching function but don't have transformers or rectifiers.

[36] In the 20th century, prior to electrification, WAB and WW class tank locomotives typically hauled suburban trains.

Prior to full electrification, services beyond Taitā were hauled by DE class diesel locomotives.

In November 2013, the GWRC voted to close it permanently as on health and safety grounds, it was too expensive and nearly impossible to upgrade the station to provide step free access via ramps for disabled passengers.

Once the west coast route of the North Island Main Trunk railway was available, all freight that could be diverted was sent via that line due to the costs and inefficiency of sending it over the Rimutaka Incline.

Today, KiwiRail freight trains operate through the Hutt Valley between Wellington and Waingawa, south of Masterton.

[37] The 2011 – 2012 Regional Rail Plan (RRP) proposed to start duplication work between Trentham and Upper Hutt in 2012.

[38] Double-tracking of the Trentham – Upper Hutt section was confirmed by GWRC in June 2014 with the adoption of the regional public transport plan.

Network extensions beyond the current Metlink rail operation limits would be by "shuttles or non-electrified services" running to Wellington.

[41] Service improvements proposed in May 2017 included double-tracking the 2.7 km of line between Trentham and Upper Hutt; for which the GWRC was seeking government funding.

Resignalling of the Woburn Junction (2021; $2.08 million) will allow quicker access to the Gracefield Branch and Hutt Railway Workshops.

[47] Work on double tracking the 2.5 km from Trentham to Upper Hutt was expected to take eighteen months, starting in October 2019.