From Kings Cross, the line proceeds west towards the Sydney Central Business District on a viaduct that passes over the suburb of Woolloomooloo and the Eastern Distributor.

Turning south, the line proceeds through Town Hall, Central and Redfern stations, before emerging behind the Eveleigh Railway Workshops.

The main line then heads in a southerly direction, parallel to the Princes Highway to the west and bordering the Royal National Park on its eastern side until Waterfall, the last suburb in the Sydney metropolitan area.

28, which provided £1,020,000 for the construction of this railway, and proposed that the first section of 37 kilometres (23 mi), constituting approximately the present suburban route, be completed by 30 September 1884.

[5] Almost immediately, concerns were raised about the new route's viability, most specifically over the cost of tunnelling between Waterfall and Otford to reach Wollongong.

Work was suspended past the 24-kilometre (15 mi) point at Como, and Government surveyors were instructed to re-survey a route via the Port Hacking River that had originally been surveyed in 1873.

The line was duplicated between Hurstville and Loftus Station (with the exception of the Como bridge over the Georges River) in April 1890, then southward to Waterfall by 12 December 1890.

[8] After duplication in 1890, the original lattice-girder Como Bridge across the Georges River was laid as gauntlet track.

[9] This arrangement remained in place for many decades, causing a notorious bottleneck on the line, until the New South Wales Government commissioned John Holland & Co to build a new bridge in 1969.

[10] Construction of the new bridge, made of prestressed concrete box girders, commenced in 1969 and was first used by the 18:17 service from Como on 19 November 1972.

[11] The old bridge, as well as a former alignment of the line between Mortdale and Oatley replaced in 1905, is now used as a rail trail for pedestrians and cyclists.

[8][13] By November 1926 the electric overhead had passed Sutherland and continued to the branch line constructed to the Royal National Park.

A single track tramway line, with four stations and a goods siding, was opened on 12 June 1911 at a cost of £37,505.

The route commenced at the southern end of Sutherland station, proceeded north-east to the Princes Highway, east along the Kingsway, then south past the site of the present rail terminus to Shelly Park in the centre of Cronulla.

Bradfield's plan entailed building a City Circle loop, with an extension through to the Eastern Suburbs by means of a viaduct over Woolloomooloo.

[21] Upon the passing of the City and Suburban Electric Railways (Amendment) Act in 1947, construction finally commenced on a variation of the Bradfield's proposal.

The New South Wales Government awarded the contract for the civil and structural design to the successful Snowy Mountains Hydro-Electric Authority.

Initially, trains ran as shuttle services between Central and Bondi Junction; it was not until a year later that work was finished to integrate the lines.

A double-track junction with the Illawarra Line at Erskineville south of Illawarra Junction, twin single track tunnels connecting to the Eastern Suburbs Railway platforms at Central, a set of underground platforms at Redfern and a turnback tunnel at Martin Place opened to complete the project on 20 July 1980.

[3] The current running operations for passenger services have remained generally unchanged since 1981 with the integration of the Illawarra line and the Eastern Suburbs Railway.

In 1980 Waterfall was electrified and replaced The Royal National Park as a terminus, having been served by a diesel-operated shuttle service until then.

In 2009–2010, 97.65% of all Eastern Suburbs and Illawarra services ran on-time, ranking it the most reliable line on the CityRail network.

The report highlighted the problems facing the network at that time and noted that capacity on Illawarra Line trains was often at 120%, and that 180% was not unexpected.

[38] To address this, the NSW Government constructed the Bondi Junction Turnback, which enables an additional six trains per hour to terminate at the station.

[40] The line between Oatley, Sutherland and Cronulla also received signalling upgrades to allow more services to run at shorter intervals.