[1] Despite having Welsh-speaking grandparents Thomas's parents did not speak Welsh as adults, and therefore he and his two sisters were raised in an English-speaking home.

Thomas later attended the Glamorgan College of Education and the University of Wales, Cardiff, where he completed an MA in the history of the Welsh language.

[2] This formed part of his chapter in the book Iaith Carreg fy Aelwyd, published in 1998, and its English-language version.

Thomas was deputy head teacher of Gladstone Primary School[3] before being elected to the National Assembly for Wales.

Thomas had been active in Plaid Cymru since his teens, filling a variety of posts from branch secretary to vice president.

[citation needed] He was a longstanding champion of the campaign for leasehold reform and a founder member of Clwb Ifor Bach[4] (Cardiff's Welsh-language night club), whose president he was from 1983 to 1989.

Thomas faced a strong challenge for the 2003 regional seat selection, but comfortably won the membership vote.