William St. Thomas Smith was born in Belfast, Ireland in 1862. and died at St. Thomas, Ontario. His family emigrated to Canada when he was young, they settled in Beaverton, Ontario. He studied at the Ontario College of Art. Apparently it was here he received the nickname of "St. Thomas" in order to distinguish himself from another student with the same name.
Smith worked in the studio of J. W. L. Forster for some time.
Smith settled permanently in St. Thomas, Ontario with his wife. In 1887 he took a positon teaching at Alma College.
He traveled widely in Canada, Great Britain and Europe throughout his life.
His work was often done in watercolour, his subject usually landscapes and seascapes.
Smith's art was exhibited at the Ontario Society of Artists, the Royal Canadian Academy, the Toronto Industrial Exhibition and many commercial galleries.
He received an honorary degree from the University of Western Ontario in 1940.
He died in St. Thomas, Ontario in 1947.