Mr. Thomas was elected to the Welsh Assembly in 1999.  In the 2007 elections he won his seat by the 2nd highest majority in Wales.
He was the Chair of CND Cymru from 1984 - 1988.  In 2003 he was appointed as Deputy Leader of the Plaid Cymru Assembly Group.  He has been the Health and Social Services spokesperson.   He was the Minister of Heritage for 12 months with responsibilities for Culture, Sport and the Welsh Language.  Mr. Thomas now sits on the Rural Development and Sustainabiltity Committee.  His political interests are Health, Social Justice and the rural economy, Europe and Transport.