[6] Merthyr RFC are recognised as one of the eleven clubs present on 12 April 1881 for the formation of the Welsh Rugby Union.

However, in 1948 a meeting governed by Cyril Williams, Monty Warrington and Ron Gethin was enthusiastically supported and the game of rugby union returned to Merthyr Tydfil.

Promotion immediately followed from the fifth to the fourth, then the third to the first in successive years (The two division jump caused by WRU restructuring of the league).

In 2013-14, the Ironmen completed a Double under the Captaincy of Steve Lang and coached by former Wales International Lee Jarvis.

The club won the WRU Principality Premiership during their inaugural season, with the final played against Aberavon RFC.