Between 1980 and 1994 Rhys Mwyn was bass player with the Welsh Language Punk band Anhrefn (trans. disorder). They toured Europe constantly and were known to play up to 300 shows a year.

In 1983 the band launched their own independent record label Recordiau Anhrefn which went on to release early records by Y Cyrff, Datblygu, Llwybr Llaethog, Fflaps and Tynal Tywyll and through the label Welsh bands began to receive recognition and encouragement beyond Wales. John Peel championed Anhrefn on Radio 1 and in all they recorded three Peel sessions between 1987 and 1993.

In 1987 Anhrefn become the 1st Welsh Language Band to sign to an International Recording Company and recorded two albums, Defaid , Skateboards & Wellies 1987 and Bwrw Cwrw 1989 for the label Worker's Playtime. In 1990 Anhrefn signed to Crai, a Label set up by Dafydd Iwan within Sain and released their best known song Rhedeg i Paris (trans. Running to Paris).

In 1993 Rhys started to work on a freelance basis for Crai signing the band Catatonia and releasing their two Eps For Tinkerbell, 1993 and Hooked, 1994. During this period Rhys also worked as acting manager for Catatonia.

In 1998 Rhys signed the band Big Leaves to Crai for two Eps and a Welsh Language album. He also signed Anweledig and Topper in 2000 and established the Miri Madog Festival at Porthmadog Sports Club with the aim of showcasing emerging Welsh talent on the music scene.

His autobiography was published by the Welsh Language Press Y Lolfa in 2006.