Tyddyngwyn was an intermediate station on the 1 ft 11+3⁄4 in (603 mm)[6] narrow gauge Festiniog and Blaenau Railway (F&BR); it opened with the line on 30 May 1868.
[8] In common with Festiniog and Tan-y-Manod stations, the only published photographs were taken from a distance, they lend the buildings the appearance of corrugated iron.
On 1 September 1882 the standard gauge Bala and Festiniog Railway reached Llan Ffestiniog from the south, enabling a passenger from (say) Bala to Tyddyngwyn to transfer from a standard gauge train to a narrow gauge train at Llan by walking a few yards, much as modern-day passengers transfer between Conwy Valley Line and Ffestiniog Railway trains at Blaenau Ffestiniog.
Tyddyngwyn's station building appears to have resembled that at Tan-y-Manod, but no details of its facilities have been published.
The line through the site of Tyddyngwyn station closed in 1961 but it was mothballed pending building the long-discussed cross-town link to enable trains to run along the Conwy Valley Line, through Blaenau and on to Trawsfynydd nuclear power station which was then being built.
The line through the site reopened on 24 April 1964, but none of Tyddyngwyn's or Manod's facilities were brought back to life.
In Spring 2016 the mothballed single track line still ran past the site to the former nuclear flask loading point.
On 21 September at least one regional newspaper reported that "Volunteers are set to start work this weekend on clearing vegetation from the trackbed between Blaenau Ffestiniog and Trawsfynydd."