In 1860, the port of Penmouth was a smallish port on the Wessex coast, with only turnpikes to get goods in from and out to the country. The port commissioners, seeing the 'success' of the London and South Western Railway's routes to the West Country, consulted with the town council of Tyneworth and other nearby local landowners on the building of a railway to connect with the nearest main line. The route decided on a connection at Sayersbridge, and construction commenced in 1861. Completion of the twenty-nine mile route was in 1863, with opening on Monday the 4th of May that year. The line was owned independently by the Sayersbridge and Penmouth Railway Company Limited (the S&PR for short, but known as 'the Sap' colloquially) but was operated by the London & South Western Railway until 1868, when the financial troubles of 1866 finally caught up with the owners and they sold out to the L&SWR.

The port of Penmouth and its town of Tyneworth flourished once the railway was running, and became quite significant both for trade and population. Most of the route served small rural village and farming populations, and private landowners, with the only intermediate settlement of any size between Sayersbridge and Tyneworth being the town of Arneford.

The earthworks of the line were for most of its length built with double track in mind, but as a cost saving measure many of the bridges were single track only, and of somewhat light construction. The plan had been to replace these once the prominence of the port increased, but with the 1866 financial crisis and the ensuing buyout by the L&SWR in 1868 and an insufficient improvement in traffic, these were never upgraded to double and the line has stayed single for its entire life. It was always mainly a freight line, but its passenger service was adequate to the modest local needs. No direct trains to London were ever run regularly, although occasionally attempts were made to do so, particularly in the 1950s when post-war holidays could be taken and visits to Sto Sands were popular. The line survived the Beeching cuts of 1963/4 due to its freight usage, but with the construction of a dual carriageway direct to Penmouth in the late 60s, the freight disappeared from the line and the remaining passenger usage was simply not enough to keep it running. So in 1974 the line was closed, despite a campaign to retain it.

The campaign to keep it open morphed into a preservation movement, and enough support was gained to prevent the wholesale selling off of the trackbed. From that point on the S&PR Preservation Society managed to slowly reopen the line, with the only track formation obstacles being a few private residence ingresses and the removal of a number of the lightweight bridges. These had been in a poor state and had been dismantled for safety. The opportunity was taken to replace them with double track bridges as each one was arrived at during the 22 years it took to get from Tyneworth to Sayersbridge. This meant that by 1996 the line's infrastructure was finally capable of double track throughout, something the line had never achieved while in national ownership! The line is currently still single track but it is now feasible to put in a second if traffic levels demand it. After privatisation of the national network in the early '90s and the reconnection with the national network in '96, the prospect of commercial freight using the line raised its head. An arrangement for regular stone traffic from Weytonwell Quarry was started in 2000, to be followed by some occasional traffic of exports and imports of bulk freight to and from the port. This has allowed the line to improve its infrastructure to allow running speeds of 50 mph. Not all stock is considered suitable for that so some services are still restricted to the 25 mph limit. With the freight traffic, consideration for doubling the line has been given, but the freight movements as at time of writing are not thought sufficient to do so and there is no benefit to the heritage operation to implement a second track throughout. There are plans to put in double track in a [couple of places] to ease operation in the Summer when both the freight and heritage operations are running simultaneously.

Additional to the loss of some of the bridges after closure, a number of the stations were demolished along with most of the original railway buildings such as goods sheds and signal boxes. These have been replaced either with imported non-S&P originals from various locations around the country, or new builds where no suitable pre-existing replacements could be sourced.

The colours of the buildings of the original S&PR were dark blue and cream. The stock was the same, with locomotives in plain dark blue, but these were repainted in L&SWR colours after the sale to that company. In SR days the station colours changed to green and cream. The preservation movement became a limited company in the early 2000s, with a rebranding exercise giving the operation the name 'Wessex Rail'. Some of the locomotives and stock have been repainted in Prussian Blue with double gold lining, the livery having been 'lifted' from the S&DJR's colours. The buildings have taken the original S&P dark blue and cream.

The line now flourishes in three ways: firstly, it's a heritage line running steam and diesel trains for visitors; secondly, it has commercial freight traffic adding a useful cashflow; thirdly, and not lastly, it now runs a scheduled service between Tyneworth and Sayersbridge using a couple of leased 'modern' units for commuter and shopping passengers.