His debut was in 1915 in the Western Lone Larry, performing under his own name. In 1925, after having appeared in many silent films, he changed his name to Tom London, and used that name for the rest of his career. The first film in which he was billed under his new name was Winds of Chance, a World War I film, in which he played "Sgt. Rock".
London was a trick rider and roper, and used his trick skills in scores of Westerns. He appeared as the sidekick to Western star Sunset Carson in several films.
London is credited in several prints of The Great Train Robbery, but since he was only 14 years old when that movie was filmed in 1903, it's unlikely that he actually appeared in it.