Iwan's earliest material was Welsh translations of songs by American folk/protest singers (Woody Guthrie, Pete Seeger, and Bob Dylan) until he began to write his first ballads.

[citation needed] By the late 1960s, he was receiving television coverage both for his music and for his political activities as a member of Cymdeithas yr Iaith.

He was imprisoned in 1970 for his refusal to pay fines for defacing English-language road signs as part of the fight for Welsh-language rights, serving three weeks of a three-month sentence.

[5] His song "Peintio'r byd yn wyrdd" ("Painting the World Green") was regarded as a "battle hymn" of the road signs campaign.

[3] During the 1970s, his political interests (and songs) took in such themes as Pinochet's Chile, Welsh devolution, the Vietnam War and the Northern Ireland troubles.

Later songs mention events such as the Tiananmen Square massacre (1989), the Gulf War (1990) and opencast mining in the south Wales valleys (1995).

[6] In January 2020, the song reached number one in the UK iTunes chart, spurred on by purchases by supporters of Welsh independence group YesCymru.

Iwan's long service to the Welsh language led to his being made an honorary member of the Gorsedd of Bards at the National Eisteddfod at Bangor in 1971.