Although much of it originated as part of the North London Railway, the current route is the result of a series of amalgamations, closures and reopenings, and has a mix of third-rail and overhead electrical power supply.

It closed for four months in 2010 between Gospel Oak and Stratford and had a reduced service for another year to allow platform extensions and signalling upgrades.

That threat, eventually lifted, led to the founding of a new campaign group, the North London Line Committee, which tried to work with British Rail management to promote the service.

These were succeeded by Southern Region Class 416 EMU for a short period, these units being allocated to Selhurst depot in south London.

The new service was branded by British Rail as the North London Link, and some signs using this name still exist.

Despite favourable performance figures,[6] the North London line used to be regarded by frequent travellers as offering a poor[7] and unreliable[8] service with extremely congested trains which were often cancelled shortly before they were due to arrive.

TfL also brought in new trains and the lines, which previously appeared on tube maps following a public campaign, gained their own colour.

TfL closed the line in February 2010 between Gospel Oak and Stratford for the installation of a new signalling system and the rebuilding or extension of platforms to allow four-car trains to run on the line; most NLL platforms had been reduced in usable length (where they had not been originally short) in the late 1960s when services were reduced to three-carriage trains only.

Trains were frequently cancelled owing to rolling stock shortages; these circumstances had begun some years earlier with service reductions and scrapping of trains in the late 1960s, followed in later years by closure of depots at Croxley Green and Stonebridge Park preventing stabling of spare stock.

Along with what eventually became a lack of trains timetabled to serve Liverpool Street to match the needs of rush-hour passengers, this inevitably led to falling patronage.

In 2000, Anglia Railways started a service between Basingstoke and Ipswich, utilising parts of the North London line.

The service was called London Crosslink and ran up to five times a day at roughly two-hourly intervals.

On the North London line, the trains called only at Stratford, Highbury & Islington, Camden Road (some services), West Hampstead and Willesden Junction.

The AC electrification of the eastern part of the North London line uses the previously unelectrified northern pair of tracks, which were also partially singled at the same time.

The river crossing is made by Kew Railway Bridge on tracks which are shared with the London Underground District line.

The line into Broad Street used third-rail supply and, when the through service to North Woolwich started in 1985, trains used the third rail throughout.

This use was steadily extended, and trains had to make a number of changes between traction current supplies during their short journey; these were at Hackney Wick, Dalston Kingsland, Camden Road and Acton Central.

With the final upgrade of the line between Camden Road and Stratford, the need to change traction current systems on this stretch was eliminated, and now the only changeover takes place at Acton Central for the short section to Richmond.

of new four-car, air-conditioned trains, combined with improved signalling and passenger information, has dramatically overhauled the service, making it an effective alternative to travelling through central London for many orbital journeys.

Maiden Lane station may be reopened by Camden Council;[16] however, the Office of Rail Regulation has not included this in the current plans.

A new park utilising the former railway alignment between Camden Town and King's Cross was given planning permission in January 2023.