John Thomas won a harp at an Eisteddfod at eleven and was sent to the Royal Academy of Music, London, where he spent eight years as student and many more as professor, afterwards joining the staff of the Royal College of Music. Thomas toured Europe as a harpist and visited the United States, adjudicating at the Eisteddfod held in connexion with the Chicago Festival of 1893. He was also a harpist to Queen Victoria.

He was a composer of symphonies, operas, cantatas, harp concertos, and other things, and a collector and editor of the old Welsh melodies. At the National Eisteddfod of 1866 John Thomas was presented with a purse of five hundred guineas for his services to the music of his country. His bardic name was ‘Pencerdd Gwalia’.