Siân Gwenllian is a Welsh Plaid Cymru politician who has represented the constituency of Arfon in the Senedd since 2016.^[1] She currently holds the seat with a majority of 8,642 votes.^[2]

She was educated at Friars School, Bangor and at Aberystwyth and Cardiff universities. She was then a journalist with the BBC and HTV in Bangor before becoming a county councillor for Y Felinheli, the village where she was brought up and currently lives.^[3][4]

Between 2010 and 2012 she was responsible for the authority's finance portfolio. Between 2012 and 2014 she was Cabinet Member for Education, lead on children and young people, and was deputy leader of the Council. In 2014, she was appointed Gwynedd Small Business Champion, responsible for promoting this sector of the economy in Gwynedd.^[3]

Siân Gwenllian represents the Arfon constituency in the Welsh Parliament. She was elected for the first time in 2016, and was re-elected in 2021.

She previously held the portfolio for Local Government, the Welsh Language, Equalities and Planning in Plaid's shadow cabinet in the 5th Senedd.^[5]

She was also a member of the Senedd's Committee for Children, Young People and Education, Finance Committee and the Senedd's Business Committee.^[6]

In 2018, she became co-deputy leader of Plaid Cymru alongside fellow Ynys Môn AM Rhun ap Iorwerth. Upon her appointment by leader Adam Price, Siân Gwenllian stated that, "I'm proud to be a member of this group of talented and skilled individuals and look forward to working together as a collective as we move towards the project of building a New Wales".^[3]

Siân was also appointed as an Senedd Commission Commissioner in November 2018 and was responsible for official languages and the delivery and transformation of services to Assembly Members.^[7][8]

From 2018 to 2021, Gwenllian was Plaid Cymru's spokesperson for the Welsh Language, Education, Children and Young People and Culture. She was also the Chief Whip and Deputy Leader of Plaid Cymru's shadow cabinet until 2023.

Siân was re-elected in 2021 with a higher percentage of the vote than any other candidate throughout Wales.

Since 2021, Siân is Plaid Cymru's Lead Designated Member in the Co-operation Agreement with the Welsh Government.^[9]

Siân had four children with her husband, Dafydd but in 1999, when their youngest son was only three years old, Dafydd died of cancer. Siân brought up the four children as a single parent.

During her time at Aberystwyth University she was President of the Students' Union. She was also a Member of the Board of Governors of schools and a Member of the Community Council before becoming a County Councillor.