The former Merthyr Synagogue is located on Bryntirion Road in the Thomastown section of Merthyr Tydfil, Wales. It is a Grade II listed building and thought to be the oldest purpose-built synagogue still standing in Wales.
The Jewish congregation of Merthyr was established in 1848 at a time when Merthyr Tydfil was a centre of the industrial revolution and the largest town in Wales. The new congregation called itself the "Merthyr Tydfil Hebrew Congregation", and erected its first synagogue in 1852–1855 in John Street. That first building was demolished in the 1990s.
The 1855 building was replaced by the prosperous congregation with the surviving synagogue building in 1872–1875. The congregation had 27 head-of-household members in 1900.
The congregation, which had been dwindling, was rededicated in 1955. In the 1980s, the congregation was closed and the building was sold and became the Merthyr Christian Centre. As of 2006 the former synagogue was in use as a gymnasium. In 2008 there was a plan to convert the building into eight residential apartments whilst preserving the exterior of this building.
The synagogue is a stone building designed in Gothic Revival style, as were the former synagogues of Llanelli and Pontypridd. Unlike the "simple," "charming" Gothic synagogues that once graced Llanelli and Pontypridd, however, the synagogue of Merthyr Tydfil is a "Disneyland" fantasy of a building that architectural historian Sharman Kadish calls a "double-turreted Gothic folly" of a building. Kadesh considers the Merthyr Synagogue to be "architecturally speaking one of the most important synagogues in the UK."
The building is four storeys high, five when the raised basement is counted. It is crowned by a high gable two-storeys tall, capped with stone finials. A double stone staircase rises to the Gothic entrance door. Two storeys above the door there is a pair of Gothic pointed-arch windows. Flanking the door and pointed-arch windows, a pair of hexagonal, stone turrets rise three storeys and are topped with hexagonal, conical roofs pointing skyward. As of 2006 the former Torah Ark has been moved into the raised basement where it was being preserved.