Built as a mix of underground, at ground level and as an elevated line, it runs through the northern part of Groruddalen, serving such neighborhoods as Grorud, Romsås and Stovner.

Proposals for an urban railway through the upper parts of Groruddalen were first articulated in public documents in 1919.

The rest of the line opened in three stages: to Rommen on 3 March 1974, to Stovner on 18 August and to Vestli on 21 December 1975.

The Grorud Line is a 13.0 kilometers (8.1 mi) and runs through the northern side of Groruddalen in Oslo.

At this point there is also a direct, single-track tunnel which allows non-revenue trains access to Ryen Depot.

[3] It continues through a short tunnel under the Alna Line and Ring 3 before reaching Økern Station.

[4] The line continues past Risløkka Station parallel to Østre Aker vei.

[11] The line continues at ground level until just before Stovner Station,[12] at which time it enters a 1,340-meter (4,400 ft) tunnel.

Operations of the lines are done by Sporveien T-banen on contract with Ruter, the public transport authority in Oslo and Akershus.

Transfer to Ruter buses are available at Tøyen, Carl Berners plass, Hasle, Økern, Linderud, Ammerud, Grorud and Stovner.

An overground system was ruled out because of the increased estimates in traffic and an underground route was instead pursued.

There was a large housing shortage in Oslo and the region was experiencing rapid population growth.

The solution was to build a series of commuter towns in Aker, which would be the basis for the traffic on the metro.

[26] The basics for the metro were established in 1951, with a common segment through Enerhaugen with a terminus at Grønlands torg, to avoid having to cross Akerselva.

The original plans called for the use of 600 to 650 volt (V) direct current (DC) fed via a pantograph, to allow comparability with the western light rail.

The system also took into use cab signaling and moving blocks, which were cutting edge technology at the time, and had only been implemented on the Stockholm Metro in Europe by then.

[30] Stations were originally planned to be barrier-free and that the operator would employee conductors on board, similar to what was done of the tramway.

Commuter towns with a mix of row housing, condominiums and high-rises were built along the line, often concentrating close to the stations.

However, lack of sufficient personnel and technical difficulties caused a last-minute shift in these plans and instead the Lambertseter Line opened on 22 May 1966.

The final opening took place on 21 December 1975 when the tunnel past Stovener was extended to Vestli.

The work involved closing the Grorud Line's southern portion between September and December 2013.

[47] Financed through Oslo Package 3 and budgeted to cost 600 million krone, the project will include the new Løren Station.

[50] In the western end of the Grorudalen, a branch from Stovner has been proposed to connect to the Furuset Line.

[52] Part of the rationale is to serve the new suburb of Skårerødgården, which is planned with 1,200 new houses, located within the catchment area of Lørenskog Station.

[53] The cost of building the 4.8 kilometers (3.0 mi) from Ellingsrudåsen to Stovner is estimated at NOK 2.4 billion.