Iwan's early career has been described as playing a major role "in mobilising the Welsh popular music scene in a nationalist linguistic direction".

During a conversation with his friend, the historian and Plaid Cymru MP Gwynfor Evans, Iwan is said to have been given the initial idea for the song, which draws parallels between what he saw as the contemporary threats to Wales and the historical threats the Welsh people had suffered, confronted, and survived since Magnus Maximus (Welsh: Macsen Wledig) withdrew the Legions at the de facto end of Roman rule.

Iwan hoped to parallel the troubles of ancient Wales with the more modern threats to the nation, to demonstrate the fortitude and survival of the Welsh culture at a time he felt it was most threatened.

[12] During the 1984-85 miners' strike, Iwan would sing "Yma o Hyd" on the picket lines on numerous occasions, as well as performing it for quarry workers and farmers.

[4] It has been suggested that the song played a "not insignificant" role in raising the morale of Welsh nationalists during Margaret Thatcher's 1980s tenure as Prime Minister of the UK.

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

Most notably, Ray Gravell would sing Iwan's songs for his Llanelli, Wales, and British & Irish Lions team mates.

[20] In more recent years has been sung by supporters of Wrexham AFC and Cardiff City FC and has also become an unofficial anthem for the Wales national football team.

[21] The players requested that Dafydd Iwan perform the song live before kick off of the penultimate game of the FIFA World Cup qualifying campaign against Austria, winning 2–1.

[13] The song was also sung live by Iwan in the final match of the campaign that saw Wales qualify for the FIFA World Cup for the first time since 1958 after defeating Ukraine 1–0.

Some moments featured include the miners' strike, Iwan being released from prison following his arrest for vandalising road signs as part of a campaign for the Welsh language and Michael Sheen's speech to the Wales squad.