[3] She was a journalist for BBC News Wales, and later worked at Academi Hywel Teifi in Swansea University, organising public events and community courses on Welsh history, culture and literature.

[5] A self-proclaimed democratic socialist, she became a member of Plaid because "[she] felt that the Labour lordship of the Gwent Valleys where [she] grew up had become a damaging hegemony, which had lost contact with the culture and people it once represented and defended."

Furthermore, Williams believes "the current UK political system does not offer the people of Wales an equitable and prosperous future.

Notably, she successfully helped to secure a reopening of the enquiry into the Gleision Colliery mining accident in Cilybebyll after campaigning alongside the victims’ families for several years.

[9] Sioned's husband, Daniel Gwydion Williams, is a professor of English Literature at Swansea University; he is also a writer and a semi-professional jazz musician.