[11] The line was constructed as a single track of 8.5 miles (13.7 km) in length laid with double-headed rails of 75 lb (34 kg) per yard and with fish joints.

[25] As per the notice, the line was to commence from the south end of Liverpool Railway Station, "and extend thence for twelve miles eight chains, or thereabouts, in a south-westerly direction, through the parishes of Saint Luke, Minto, and Saint Peter, to the Town of Campbelltown, and ending at the south fence of a lane on the property of Charles Morris..."[23] The line was to not exceed a gradient of 1 in 100 and the smallest radius of a curve being 30 chains.

[26] The railway is to be, "a single line throughout, laid with the double-headed rail, 75lbs to the yard, on cross sleepers, with chairs, and fish jointed.

[29] Scott and Jolly had constructed a large sawmill at Cabramatta and sourced wood (primarily Ironbark) from the nearby forest.

"[31] Randle, having been able to keep to the scheduled completion date of 1 September, offered to continue the construction of the line through to Campbelltown at the same cost per mile.

[37] On 29 August 1857, it was reported that the construction of the railway was advancing rapidly and that, "...there are a great many men already at work clearing the most woody portion of the line, about four miles from here, the real track is now easily to be traced by the formidable looking posts erected for the electric telegraph.

[40][41] On 17 April 1858, a navvy (by the name of "Romilly") working on the construction of the extension was killed when, "a truck of sleepers passing along the rail by mischance overturned upon the unfortunate man.

The Commissioner stated that the extension to Campbelltown and then onto Menangle would, "have intercepted the traffic of the Southern Road, and made the present lines remunerative.

The Government would thus have been placed in possession of information that would have fully determined the question of railway extension as applicable to the present wants of the colony.

"[52] Despite delays, and even before the government had announced the exact path of the line, anticipation for it could be seen in advertising of property and housing near Menangle.

[54][55] On 16 November 1857, the government projected the cost and constraints for the line to, "not exceed £10,000 per mile; the worst gradient being 1 in 80, and the smallest radius of a curve 40 chains.

"[56] Proclamation of the line was made 4 November 1858 and published the following day as, "to make and complete that portion of the Great Southern Railway, commencing near to the Campbelltown Station, in the parish of St Peter, and county of Cumberland, at a point marked A on the proclaimed Plan, and terminating near to the Nepean River, at a point marked B on the proclaimed Plan, in the parish of Menangle, and county of Cumberland, being a distance of five miles and sixty chains.

Rhodes criticised the Engineer-in-Chief of withholding rails and expressed, "remonstrances [...] that the timber bridges proposed for the lines would not be sufficiently strong for the traffic they would have to carry.

[63] By 13 March 1860, the progress of the extension was characterised as, "generally a forward aspect, and, with the exception of the bridge over the Nepean, that portion of the line might be completed within four months.

The formation of the line as far as the Camden road has for a long time been finished, and is ready for the ballasting and permanent way; and temporary rails have been laid down for the convenience of the contractors.

[71] At the northern end of the river, a platform was constructed at a terminus of the line to allow passengers to board and alight from the train.

[74] The complete opening of the line to Menangle was unexpectedly delayed due to the loss of the ship containing the iron girders for the northern span of the bridge.

[76] This was to be part of the extension of the Great Southern Railway from Campbelltown through to Picton and was to extend the line 6 miles and 42 links (9.5 km) from Menangle.

Upon the turning of the sod, "three cheers were then given for the Queen, three for success to railways, and three for the contractors, which, being suitably acknowledged, the company partook of a well-served collation, and left highly pleased with their visit.

The banquet was situated to the right of the station near the road with a, "marquee, with long tables, and capable of seating three hundred persons, and in an adjacent paddock were congregated the German band and numerous groups of navvies and their friends and spectators.

"[86] On 5 April 1855, a letter to the editor was published in the Sydney Morning Herald that proposed building a railway to the Fitzroy Ironworks and Coal Company in Nattai.

It was noted that, "it is felt, however, that any more than ordinary energy of action would tend to raise labour rates, and this, the process at which contracts have been taken, will not admit of.

Progress was expected to be, "pushed on more rapidly upon the completion of four steam cranes, two locomotives, and other machinery, which are being made for the contractors and the use of which will greatly facilitate the execution of the works.

"[96] Subsequently, steady progress was reported for the remainder of 1864 and 1865[96][97][98] and by November 1865, rails were being delivered to Picton for laying on the freshly ballasted permanent way.

[99] However, the final section to the Fitzroy Ironworks required heavy earthworks, "the execution of which will delay for many months the opening of the railway to Mittagong.

[106] This line was extended to Goulburn in 1869, Yass Junction in 1876, Galong, Harden-Murrumburrah and Cootamundra in 1877 and Junee and Bomen (on the north bank of the Murrumbidgee River) in 1878.

[108][109] Victorian Railways' North East 1,600 mm (5 ft 3 in) gauge line was extended from Wodonga to Albury in 1883.

[120][121] The main line south of Junee was substantially upgraded in 2007 and 2008, including the construction of passing loops up to 7 km (4.3 mi).

NSW TrainLink diesel railcars operate south from Campbelltown to Goulburn on an irregular frequency as part of the Southern Highlands Line.

Between April 1962 and August 1991, the Main South was served by the Intercapital Daylight, a locomotive hauled limited stop passenger train.