The present narrow gauge South Tynedale Railway occupies the track bed of the defunct standard gauge Newcastle & Carlisle Railway (N&CR). Created in 1825 to construct a line between Newcastle upon Tyne and Carlisle. The railway was built in stages reaching Newcastle in 1851. A branch from Haltwhistle built south to reach lead mines around Alston opened in 1852. The North Eastern Railway (NER) took over the N&CR in 1862 which subsequently became British Rail (BR) who closed the Haltwhistle to Alston branch line in 1976.

The South Tynedale Railway Preservation Society was formed in 1973 setting up the South Tynedale Railway Company with the intention of purchasing the branch from British Rail. However, before that deal could be completed BR removed the tracks. As a result the society decided in 1977 to construct a narrow gauge line and opted to obtain a short section of right-of-way between Alston and Gilderdale. With the BR closure the right of first purchase went to the counties of Northumberland and Cumbria so the Society secured a lease of the line between Alston and Gilderdale in 1980.First track was laid on 3 May 1980 a distance of 36 feet. Through 1981 and 1983 track laying reached Gilderdale Halt. Repairs to the Gilderdale Viaduct delayed start of passenger services until 30 Jul 1983. By 1987 well over 10,000 passengers a season were carried.

Work continued with the intention of reaching Kirkhaugh which lies about halfway between Alston and Slaggyford. Construction was delayed due to the poor condition of the small Whitley Viaduct, about a half mile north of Gilderdale, which required major repairs. Train service to Kirkhaugh commenced 4 Sep 1999 with the resulting closure of Gilderdale Halt.

During the winter of 2010/2011 a private construction company began building a new platform at Lintley Halt, the next destination for the railway north of Kirkhaugh. The spring and summer of 2011 saw the track laid from Kirkhaugh to Lintley. By November 2011 the main line had been laid so a special train was run to Lintley although a run-around track was not yet in place. Volunteer workers finished the work in time for Lintley station to open on 1 Apr 2012.

Next target for the narrow gauge railway was Slaggyford. Slaggyford station, originally built in 1890, consisted of a wooden station building. Now renovated and cleaned up it is used by the South Tynedale Railway as their current northern terminus. The original Station Masters house is also located here but was sold to a private individual upon the BR closure of the branch in 1976. The original standard gauge NER signalbox is long gone but a replica has since been re-constructed. The first new passenger service from Alston arrived at Slaggyford on 24 Jul 2017.
 

Are we done yet? Absolutely not...  the South Tyndale Railway's intentions are to continue the railway north from Slaggyford to Haltwhistle. South Tynedale Railway has secured a seven metre wide strip of land at Haltwhistle station following the old line of BR's Alston branch. Talks with Network Rail for access by South Tynedale trains to the platform at Haltwhistle are ongoing. A significant hurdle to be overcome in connecting the line with Network Rail is due to construction of the A69 Haltwhistle Bypass Road which has created a cutting through the old railway grade slightly south of the old brick arch railway bridge, or viaduct, over the South Tyne River. The abandoned railway grade lies several feet above the roadway so it appears a railway overbridge will have to be built to gain access to the abandoned South Tyne River viaduct and Haltwhistle station.