Opening in segments between 1884 and 1893, the South Coast railway line was built primarily to service the Coal Cliff Colliery, in which colonial government ministers and legislators were shareholders and as an economic link between the Illawarra and Sydney.

It later connected the later industrial works at Port Kembla to the greater metropolitan freight railway network in Sydney.

In 1873, the committee asked the Government Surveyor, R. Stephens, to examine the area between Sydney and Bulli for a suitable route.

Stephens noted his concerns about the Gymea Bay-Port Hacking route in a letter to the Engineer-in-Chief of the New South Wales Government Railways, John Whitton:[1]

[The country] consists of a sort of plateau or tableland about 200 ft (61 m) above sea-level, and deeply indented with numerous deep chasms and narrow ravines, the bed of whose creek is, to all intents and purposes, on the same level as the sea... Mr Carver, previous to my arrival, attempted to overcome the difficulty by heading up all the creeks, and he ran a trial line upwards of eight miles (13 km) in length, but this brought him to the summit of the range from which there was no getting down.Similar things were written about the route along the River itself:[1]

[There was] a confused jumble of huge boulders and rocks covered with thick brushwood closely interwoven with vines and creepers... a quarter of a mile per day of setting out is the most I can manage..."Besides the terrain, problems were also found with the proposed descent from Bulli to Wollongong.

Stephens found that any proposed railway would have required a series of zig zags to enable trains to climb the Illawarra escarpment.

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.

[2][4] 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.

[5] With new contractors hired, the line was completed to Hurstville in 1884, Sutherland in 1885, Waterfall in 1886 and Clifton through to Wollongong and North Kiama (Bombo) in 1887.

[6] The missing Waterfall to Clifton section comprised four large brick-arch culverts (and many small ones) and eight tunnels with a total length of over 4 km (2.5 mi), delaying its opening until 1888.

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] 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.

[11][12] The main problem was the 1,550-metre (5,085 ft)-long Otford Tunnel, which took the railway through Bald Hill from the coast at Stanwell Park to the Hacking River valley.

The steep grade and tight clearances meant that soot, smoke and heat could become unbearable, especially when a south-easterly wind blew into the southern portal or when a train stalled in the tunnel.

Though the air was hot from passing around or through the ash pan, it was nonetheless welcome.Attempts were made to overcome the problem with a ventilation shaft and chimney in the early 1890s and a blower system installed in 1909.

[7][17] By November 1926 the electric overhead had passed Sutherland and continued to the branch line constructed to the Royal National Park.

[19] Dunmore was also closed in November 2014, replaced by Shellharbour Junction, after rising commercial and residential development in Flinders and Shell Cove and their distance from Dunmore station, prompted the Government of New South Wales to build a replacement station closer to the area of urban growth.

[20] In 1917 the Thirroul Locomotive Depot opened to service the steam trains on the South Coast line and it closed in 1965.

Major structural problems with the Stanwell Creek viaduct were identified in late 1985, with one span close to collapsing and another badly cracked, requiring substantial repairs and stabilising work.

The Illawarra line continues south as four tracks through a rock cutting to the stations of Arncliffe, Banksia and Rockdale.

The line then proceeds through several tunnels down the Illawarra escarpment through the hamlets of Otford, Stanwell Park and Coalcliff.

[26] The line passes south through Albion Park (where another crossing loop is provided) to reach Kiama the extent of electrification.

[40] In 1897, land was set aside near Sutherland Station for a denominational cemetery; it was an alternative to a site at Kurnell, which would have required a long branch line.

[42] In 1886 the need for a training ground for the New South Wales infantrymen, riflemen and artillery, prompted the construction of a short branch line into the National Park.

In 1946 a second platform was added on the branch to serve the New South Wales State Scout Jamboree held between December 1946 and January 1947.

Although the branch lay dormant for some time, Parliamentary approval was subsequently given to the Sydney Tramway Museum to operate the line.

[45] The Museum converted the branch to light rail standards in order to run their trams on it, and the line was reopened on 1 May 1993,[17] marketed as the ParkLink service.

The line is double track as far as just west of Port Kembla North and is used by freight trains as well as local passenger services.

[47] The South Coast line passenger services currently consist of electric double deck multiple unit trains that operate between Bondi Junction or Central and either Wollongong, Kiama or Port Kembla.