Its numerous branches also connect the main line to Southminster, Braintree, Sudbury, Harwich and a number of coastal towns including Southend-on-Sea, Clacton-on-Sea, Walton-on-the-Naze and Lowestoft.

The line is also heavily used by leisure travellers, as it and its branches serve a number of seaside resorts, shopping areas and countryside destinations.

The first section of the line, built by the Eastern Counties Railway (ECR), opened in June 1839 between a short-lived temporary terminus at Devonshire Street in the East End of London and Romford, then in the Havering Liberty in Essex.

The London terminus was moved in July 1840 to Shoreditch (later renamed Bishopsgate), after 1900 in the Metropolitan Borough of Bethnal Green, and at the eastern end the line was extended 6 miles (9.7 km) out to Brentwood in the same year.

The section of line between Colchester and Ipswich was built by the Eastern Union Railway (EUR) to standard gauge and opened to passenger traffic in June 1846.

It was also in this year that two extra tracks were added between Bethnal Green and Liverpool Street which were for the use of West Anglia Main Line services.

In 1902, the quadruple track was extended from Seven Kings to Romford, but it wasn't until 1913 that four-tracking out to Shenfield was suggested and the First World War caused delay to this plan.

Plans were drawn up in the 1930s to electrify the suburban lines from Liverpool Street to Shenfield at 1,500 V DC and work was started on implementing this.

[11][12] The British Railways 1955 Modernisation Plan called for overhead line systems in Great Britain to be standardised at 25 kV AC.

[13] By the late 1970s, the costs of running the dated mechanical signalling systems north of Colchester was recognised and, in 1978, a scheme for track rationalisation and re-signalling was duly submitted to the Department of Transport.

The system uses BR Mark 3 solid state interlockings, predominantly four-aspect signals and a combination of Smiths clamp-lock and GEC-Alsthom HW2000 point machines.

The GEML has a loading gauge of W10 between Liverpool Street and Haughley Junction (approximately 13 miles 63 chains north of Ipswich) and from there is W9 to Norwich.

At Shenfield, the line to Southend Victoria diverges and the main-line route drops from four tracks to two; this arrangement continues for the vast majority of the way to Norwich.

[28] During the excavation of the tunnel, many important fossils were discovered, including rhinoceros, lion and mammoth; the site was known as the "Stoke Bone Beds".

Due to this, as well as traffic demands growing throughout the 21st century, the traction supply feeding arrangements are complex and somewhat unintuitive with several seemingly redundant features.

The low voltage AC utilised broadly the same substations, grid connections, OLE components and electrical clearances as the previous DC system.

In 2022, a small section between Bow Junction and Gidea Park was upgraded to a 2x25kV AC autotransformer system in order to support the Elizabeth Line service.

[39] On board the train, the operation of the dual-voltage mechanism depended on the action of the main air-blast circuit breaker and voltage-sensing relays.

When passing the first APC magnet, detection equipment fitted to the bogies would activate the circuit breaker cutting all power to the train.

Once the train had passed the neutral section, the second set of APC magnets are detected by the bogie-mounted inducers which causes a lock to be released on the circuit breaker meaning its reclosing would be under the control of the voltage-detection equipment.

The conversion of both these classes of train involved significant interventions particularly the relocating of the pantograph to a different carriage and the associated internal layout changes this caused.

[41] Neutral sections are, or course, still required on the modern 25kV system and APC magnets are still used to automatically trigger the opening of the train's circuit breaker so that an arc is not caused at OLE when the pantograph travels between live and earthed wire.

Pudding Mill Lane ATFS also feeds the Crossrail core from that point to the Westbourne Park tunnel portal and towards Abbey Wood.

[44] The original 1.5kV DC system of 1949 used traction substations at Bethnal Green, Stratford, Chadwell Heath, Gidea Park, and Shenfield all supplied by 33kV 3 phase AC distribution ring owned and operated by the railway.

[45] Beyond Shenfield, the DC system installed in 1956 to Chelmsford and Southend Victoria did not use the railway distribution lines but were connected directly to the public utility grid at 33kV.

Electric locomotives replaced diesel haulage from the mid-1980s, when the remainder of the GEML was electrified north of Colchester; their utilisation continued until March 2020.

Push-pull services were introduced during their tenure, initially using a DBSO coach at the Norwich end and latterly with Mark 3 Driving Van Trailers, cascaded from the West Coast Main Line.

Freight services also operate frequently on the Great Eastern Main Line, with its easy access to the Port of Felixstowe.

A limited number of weekend (and when engineering work is planned) c2c services, operate on part of the line between Stratford and Liverpool Street.

Additionally, a very limited number of main-line services call at Ilford, Seven Kings and Gidea Park during early mornings and late nights, often for the convenience of train drivers who may be working from these locations.