William Thomas Horton was born in Brussels on June 27, 1864 and spent most of his childhood there; his family later moved to Brighton, where he attended the Brighton Grammar School. He then worked for a Brighton architect and studied building-construction at a local art school.

Horton was one of the Smithers People, a number of artists sponsored by Leonard Smithers (1861–1907). Some starry names were in his orbit, including the writers Oscar Wilde and W. B. Yeats. In 1896 he launched The Savoy, a culture magazine that counted Aubrey Beardsley as art editor and for which Horton was a frequent contributor.