Born in Tanygrisiau, Gwynedd, and brought up there and in Blaenau Ffestiniog, Thomas was educated at Ysgol Sir Ffestiniog, University of Wales, Bangor and Jesus College, Oxford;[3] Prof Thomas was Emeritus Professor of Welsh at the University of Wales, Bangor.
As Welsh National Poet, Thomas was commissioned to write five stanzas celebrating the opening in June 2009 of Hafod Eryri, the new summit building at the top of Snowdon.
Inscribed on the buildings and windows, in both English and Welsh, they read:[6] The summit of Snowdon, here you are nearer to heaven The rocks record the aeons of creation It's our duty to guard this glory Here you will see tempests and tranquillity
All around us are the grandeur and the anguish of an old, old nation Thomas and Margaret Jones won three annual Tir na n-Og Awards from the Welsh Books Council for the previous year's best Welsh-language children's nonfiction book.
Their award-winning collaborations were Culhwch ac Olwen in 1989, Chwedl Taliesin in 1993, and Stori Dafydd ap Gwilym in 2004.