John Charles Thomas was born in Meyersdale, Pennsylvania. He was the son of a Methodist minister of Welsh descent while his mother, of German immigrant stock, had been an amateur singer. After studying initially for a medical career, Thomas won a scholarship to the Peabody Institute in Baltimore in 1910. He remained there for two years, receiving vocal tuition from Adelin Fermin.
In 1912, Thomas left the Peabody and toured briefly with a musical troupe.