Due to the death of one of their players, rugby in Llandeilo appeared to wane and the game lost support.

Competitive Rugby was first played by Llandeilo in the 1877–78 season when the club entered the South Wales Challenge Cup competition as one of the inaugurating teams;[3] and on 12 March 1881, Llandeilo RFC was one of the eleven clubs who met in Neath to found the Welsh Rugby Union.

The advent of association football was a particular draw to the youth of the town and Llandeilo RFC were forced into liquidation and they did not renew their membership of the WRU.

After World War II, Llandeilo RFC applied to and successfully joined the Llanelli and District Junior Rugby Union.

In 1949 Llandeilo were once again members of the WRU and during this time club membership flourished; and in 1954 the club became members of the West Wales Rugby Union in 1954, but their progress in the West Wales Rugby Union was fairly poor over the next ten years without any significant success.

In the 1986–87 season, Llandeilo RFC won Section E of the West Wales Rugby Union Championship.