Merthyr Tydfil (UK Parliament constituency)

Merthyr Tydfil was a parliamentary constituency centred on the town of Merthyr Tydfil in Glamorgan. From 1832 to 1868 it returned one Member of Parliament (MP) to the House of Commons of the Parliament of the United Kingdom, and in 1868 this was increased to two members. The two-member constituency was abolished for the 1918 general election.

A single-member constituency (known as Merthyr) existed from 1918 until 1945 and, by the 1950 general election, it had been renamed Merthyr Tydfil. The constituency was abolished for the 1983 general election, when it was largely replaced by the new Merthyr Tydfil and Rhymney constituency.