He was the Plaid Cymru National Assembly for Wales Member for Carmarthen East and Dinefwr from 1999 to 2016, when he did not re-stand for election.

Thomas is a Minister of Religion, the director of a language consultancy, a former Chair of CND Cymru and Welsh spokesperson for the Forum of Private Business.

[3] In November 2008, having travelled to the Gaza Strip alongside other European politicians, Thomas called for the international community to talk to the Palestinian group Hamas.

"[4] In December 2016 Thomas announced that he would stand as a candidate for election to Carmarthenshire County Council, contesting the St Clears ward.

At the Academi 2008 Wales Book of the Year ceremony, Thomas incorrectly announced that Tom Bullough was the winner.