He was born in Blaina, Monmouthshire, to Thomas and Ann.
His voice was discovered at the Ammanford Eisteddfod, and the local community of Blaina collected money for him to be trained at La Scala Milan.
Mostyn has his debut as Tonio in Pagliacci (Leoncavallo) in 1929.
He sang leading baritone roles all over the world, settled in America and married a wealthy American widow.
[citation needed] On February 13, 1923, Mostyn Thomas sang Dafydd y Garreg Wen to inaugurate the first radio broadcast by BBC.