It began as a horse tramroad in the 1850s, connecting the slate quarries in the districts around Corris with the estuary of the Dyfi river at Derwenlas. In 1878 the line was upgraded by its new owners, the Imperial Tramways Company and steam locomotives were introduced. At the same time the line was cut back to Machnylleth where it met the standard gauge main line of the Cambrian Railways. Passenger services were also introduced at this time.
The line continued on through the decades, serving quarries around Corris and Aberllefenni. After World War I, slate traffic began a slow steady decline as cheaper foreign slate and alternative roofing materials became popular. The railway went into a similar decline, with passenger service being withdrawn in 1930. This coincided with the railway being purchased by the Great Western Railway, and eventually in 1948 became part of British Rail. Following a disastrous flood on the River Dyfi that year the line finally closed.
The two remaining locomotives and several goods wagons were purchased by the newly preserved Talyllyn Railway which shares the unusual 2'3" gauge. This stock is still in operation just over the mountain at Tywyn.
In 1966 a group of dedicated enthusiasts formed the Corris Railway Society with the hope of reviving the original Corris Railway. Through years of hard work and dedication they acquired the line's original workshops at Maespoeth and the trackbed between there and Corris, just under a mile to the north. In 1985 the first official train was run back to Corris. In the summer of 2002 passenger services resumed after a break of 72 years. The society is currently building a new steam locomotive, a replica of the original Kerr Stuart 0-4-2ST No.4 (now running as Edward Thomas on the Talyllyn Railway). It is also actively pursuing a southwards extension towards Machynlleth.