The South Wales Railway opened in 1852 and unleashed the commercial potential of Carmarthen. Local boosters dreamed of pushing a connecting line up through the Tywi and Teifi valleys to a great new port at Cardigan. The Carmarthen and Cardigan Railway took the dream on but the Welsh hills did not co-operate. The Gwili valley was difficult, the Pencader Tunnel was expensive, and by 1864 the company had only laid track as far as Llandysul, sixteen miles short of Cardigan. It collapsed financially soon after. The Tivy Side Railway Company tried to push the line on to Newcastle Emlyn; the project got as far as an authorising Act of Parliament and no further. The line was leased and then absorbed by the Great Western Railway by 1882. Even with GWR money behind it, the extension to Newcastle Emlyn took until July 1895 to complete. By then the GWR had reached Cardigan from a different direction entirely, via Whitland, and the original Teifi Valley scheme made no commercial sense to push any further. The line stopped at Newcastle Emlyn and there it stayed.

The branch line carried passengers for less than sixty years. Withdrawal of passenger services came on 13 September 1952, a typical fate for rural British railways in the Beeching era and before. Freight kept the line alive a little longer, principally for the milk trains that hauled tankers of dairy product down from the Newcastle Emlyn creamery to the main network at Carmarthen. When the creamery's production methods changed and the milk traffic disappeared, the line lost its last reason to exist. Goods services ended in September 1973. The track was lifted in 1975. What remained were the earthworks: embankments, cuttings, bridge abutments, the slow physical persistence of a route that had been a hundred years in the making and was gone in a generation.

Preservation efforts began under Dr George Penn while the track was still down. The original goal was to run a standard-gauge heritage line, the way the Gwili Railway had managed at Bronwydd Arms further down the valleys. Funding could not be raised in time; the Newcastle Emlyn branch was lifted before the project could buy it. So the preservationists shifted strategy. Rather than restore the original standard-gauge trackbed, they would lay narrow gauge - 2-foot - on the alignment at Henllan, the line's one intermediate station, and run a tourist railway in miniature on the alignment of the dead branch. The first short section opened. It was extended in 1989 to Llandyfriog, and again in 2006 along the original alignment to a point where a missing bridge once spanned the Teifi - the present terminus, named Llandyfriog Riverside.

By 2014 the railway had lost its trained staff and its volunteer base, and an Office of Rail Regulation inspection raised serious concerns about track condition. The directors tried to outsource operations to a local businessman, who promptly lifted much of the track between Henllan and Pontprenshitw, ran tractor-hauled carriages he called a land train, sold off rolling stock, and felled trees for the timber trade. Heavy lorries removing the wood damaged the remaining track. When the businessman went bankrupt and walked away, the original managers returned in 2015 to assess the damage. They relaid a kilometre of track to ORR standards, recovered what rolling stock they could, and reopened in 2016. The line that runs today is a fragment of a fragment - perhaps a quarter of the longest extent of the heritage railway, perhaps a hundredth of the great Carmarthen-to-Cardigan line that nineteenth-century Welsh boosters dreamed of. But it still runs. Out of Henllan, across Bridge 55, the little arched span they call Mini-Pont, the train threads the same valley wall its predecessor used 130 years ago, on tracks half the width, for an entirely different purpose, and with no remaining illusion that it might one day reach the sea.