He was born in Bridgend, on Saint David's Day, 1 March 1826, son of a tailor, also named John Thomas, a clarinetist in the amateur town band. He was the eldest of seven children, four of whom also played the harp, most notably his brother Thomas Thomas. John Thomas started off by playing the triple harp which had three sets of strings and was very difficult to play. At the age of 14, through the influence of Ada Lovelace (Lord Byron's daughter), he was admitted to the Royal Academy of Music in London. His teachers there included Cipriani Potter for composition.
He wrote many pieces for the harp that are very popular today and are used in the exam syllabus. He also wrote an opera, a symphony, two harp concertos, overtures, chamber music, and two cantatas – Llewellyn (1863) and The Bride of Neath Valley (1866). He played one of his own harp concertos at a Philharmonic concert in 1852.
John Thomas: Welsh Music for Voice and Harps: Hela'r sgyfarnog. Gogerddan. La primola. Cambria. Ymadawiad y brenin. Serch hudol. Hob a derry dando. Souvenir du nord. Dadl dau. Bedd Gelert. Thou art the star. L'adieu. Rachel Ann Morgan, Edward Witsenburg Globe Classics. 2012