[7] The government acquired the Wellington and Manawatu Railway Company on the 7 December 1908 and incorporated it into its national network as the southern portion of the North Island Main Trunk line.

Paekakariki became a major station where long-distance trains swapped from steam (later diesel) to electric motive power and became the northern terminus of the commuter line for many years.

[4] The W&MR constructed the line as a single-track railway with crossing loops at principal stations to allow opposing trains to pass.

[15] In conjunction with the extension of electrification to Paraparaumu in March 1983, double-track was extended from Paekakariki to Mackays Crossing on 5 December 1983.

They had been ordered to replace the wooden carriage trains hauled by electric locomotives on commuter services and largely displaced the DM/D units on the Paraparaumu Line.

[4] Completion of the project was delayed to 2011 to minimise commuter disruption by working in the quiet end-of-year holiday period, according to ONTRACK programme director David Gordon.

The project involved 50 workers and 20 machines installing 600 traction poles in eight or nine metre deep holes, and laying 30 km of rail and 30,000 sleepers.

Upgrading Waikanae station rather than moving it south of Elizabeth Street or providing a road underpass was criticised locally, as frequent closing of the Elizabeth Street level crossing south of the station (which connected to State Highway through the town) could increase traffic congestion in Waikanae.

The substations are located at Wellington, Kaiwharawhara, Glenside, Paremata, Mana, Pukerua Bay, Paekakariki, Raumati, Lindale and Waikanae.

Also along the line are two "cross-tie" substations at Ngauranga and Tawa, which provide a switching function but don't have transformers or rectifiers.

Public road-rail crossings have warning lights and barriers, and some are now fitted with automatically locking pedestrian gates to prevent use while alarms are operating.

Proposals for new stations at Raumati South, between Mackays Crossing and Paraparaumu, and Lindale, north of Paraparaumu near Otaihanga, were on hold, to be reconsidered after 2010, as it was claimed that there were problems affecting a station at Raumati (the provision of access to SH 1 and park-and-ride facilities) and an unstable hillside behind the line.

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

[25] Proposed infrastructure upgrades include sleeper replacement in tunnels, stabilisation of high-risk slopes and renewal of one bridge with timber elements.

[34] This could be a "final nail in the coffin" for the under-threat Capital Connection service from Wellington to Palmerston North, which also stops at Ōtaki.

[34] During the 2017 general election, the Green Party proposed extending electrification to Ōtaki as an alternative to the Northern Corridor extension from Pekapeka.

[35] In the lead up to the local authority elections of 2019, candidate for Mayor of the Kāpiti Coast District, Gwynn Compton, started a petition to extend electrification to Ōtaki.