Dafydd was born into a family of Norman ancestry in Hanmer, in Flintshire (now Wrexham County Borough), north-east Wales.
However, Dafydd was moved to compose an elegy for his friend, the harpist Siôn Eos, who was hanged for killing a man in a tavern brawl.
In this, arguably his finest poem, Dafydd expresses his own anti-English sentiment, and regrets that Siôn Eos could not have been sentenced under the more humane Welsh Laws of Hywel Dda, resulting in compensation being paid to the victim’s family rather than being sentenced to the death penalty under cyfraith Lundain ("London’s law").
This was achieved with a cywydd in praise of the Trinity, which exemplified the 24 metres of Welsh bardic poetry reformed by Dafydd, previously codified by Einion Offeiriad and Dafydd Ddu o Hiraddug.
However the consequence of this, and of Dafydd in particular, was that greater emphasis was placed upon the bardic craft with its adherence to the stricter metres rather than on the content and theme of the poems.