English-born Thomas moved to Montreal, Canada in 1909. He was completely self-taught and became a protégé of Canadian wunder-pianist Willie Eckstein. He filled in for Eckstein at the Strand Theatre, and shared a weakness for alcohol with Eckstein.

His first piano rolls were issued in 1916 for QRS and Aeolian and were recorded during a US visit. He also recorded a 78 of his own 'Delirious Rag' and 'Classical Spasm' for Victor in 1916.

Around the same time he became resident pianist at the Regent Theatre in Montreal, and more 78s followed by the Harry Thomas Trio, also featuring a vibraphone and sax.

The advent of talking pictuers reduced Thomas to playing in seedy nightclubs, and in 1941 he died in hospital from an alcoholic-induced infection. Eckstein was one of the few mourners at his funeral, and his grave marker at the Cote des Neige Cemetery was later removed for non-payment of fees.