Trelewis is a small village in the Taff Bargoed Valley of south-east Wales, currently located in the southern part of Merthyr Tydfil County Borough.

It is a former mining village and together with nearby Bedlinog was until 1974 part of the Gelligaer Urban District Council area of the county of Glamorgan.

The Council was created in 1974 by the former Gelligaer Urban District Council prior to its abolition and the subsequent transfer of Trelewis and Bedlinog into the Merthyr administrative area upon local government reorganisation in that year, to which most people in Bedlinog and Trelewis were opposed.

Bedlinog is to the north of Trelewis on this line, whilst Nelson is to the south.

Trelewis Welfare, a former member of the Welsh Football League, played in the village.