The expanding Kimberley Diamond Boom in the early 1870's made it essential for the Cape government to secure a rail link to the north. An obstacle to achieving this was the lack of a suitable route over the folded belt mountains of the Cape.

After an earlier failed attempt to locate a route, the Hex River Pass route was re-examined in 1874. The appointed surveyor, Wells Hood, under the instruction of the railway engineer Thomas Brounger, found a potential route which snaked up 2,353ft (735m) from Worcester to the top of the Karoo mountains east of the Hex River Valley, with gradients no more than 1:40 (which is very steep by modern standards). In addition, he proposed that a short tunnel would be required.

Thomas Brounger's route through the Hex River Pass was selected by 1876 with the line to follow the route from Worcester through De Doorns, Touws River, Matjiesfontein and on to Beaufort West.

As with most early railway lines in the country, the route served an important role in the development of these Karoo towns.

The then standard wide gauge track of 4'8" could not be accommodated economically on the tight bends of the Hex River Pass. A decision was thus made by the Cape Government to install the track at 3'6". Subsequently a decision was taken to convert all tracks to the Cape Gauge of 3'6". In further efforts to construct the pass cheaply and quickly, sleepers were laid on the ground without ballast in certain areas and had to be corrected later. The maximum possible gradient and tightest curves were used to avoid extra work and expense. Between 600 and 1000 English "Navvies" were brought out to work on the construction of the line under Brounger and his railway contractor, Pauling. High wages had to be paid to these English labourers who specialised in road and rail construction. Construction of the pass went extremely smooth. The route was prepared, cut and filled well in advance of the rail being laid. Permanent way materials were transported on a construction train. Empty trucks, retrning to Worcester, were used by locals as a convenient means to transport produce from the more remote mountain farms into town.

Despite its quick and cheap construction the pass served for over 100 years. It was the starting point of the country's first railway line to the Rand and opened the way for Rhodes' colonization thrust into central Southern Africa.

The line was used to transport British soldiers during the Boer War and was a strategic target. With respect to the Hex River Pass, bridges were guarded by the British soldiers and the remains of the stone forts at these points are still evident. In 1914 a large troop train carrying a regiment of the Kaffrarian Rifles derailed on a steep downward bend on its way to Cape Town. Ten non-commissioned officers were killed. A monument to the regiment has been erected at the point of derailment.

An additional main line between Kleinstraat and Matroosberg was constructed in 1931. The original line has since been decommissioned and all permanent way material removed.

Shortly before the end of World War II, the South African Railways began to plan ways of shortening the route by tunneling through the mountain. The Hex River Tunnel scheme was started in 1945, but was abandoned 3 years later due to a lack of funds. Instead, the pass was electrified and operated with class 4E electric locomotives, which were amongst the most powerful electric locomotives in the world at that time. These were used at the head of the heavy freights such as the old Blue Train, the Trans Karoo and the Orange Express Passenger Trains.

On November 27th, 1989 the new Hex River Tunnel was opened. It cut 8 km and 112m of false rise off the old route with substantial reduction in curvature. With the opening of this route, the old Hex River Pass line was closed and the electrification infrastructure removed.