He was born in Ireland of Welsh parents, sent to boarding school in Wales, ran away from school at age 13 and went to America, where he supported himself with a series of odd jobs, including as a construction worker on the Brooklyn Bridge. He went to Chicago and worked in the meat packing industry, then went west and became a cowboy. He earned a law degree at the University of Kansas and settled down to practice law.
That didn't last long though, and he returned to England, then traveled throughout Europe. He worked as a foreign correspondent for American newspapers, then became editor of several London papers before settling in at the Saturday Review. Beginning in 1908, Harris started writing novels and other books. Among them were The Bomb (1908), The Man Shakespeare and His Tragic Life Story (1909), and The Yellow Ticket and Other Stories (1920).
In 1914, Harris came back to America. He became editor of Pearson's Magazine, which had a slightly socialist bent to it. Once, during World War I, an issue of the magazine was banned at the U.S. Post Office because of its political content. However, the magazine continued to survive during the war years, despite the dim view many took of the leftist press at the time. Harris became an American citizen in 1921.
In 1922, Harris went to Germany to arrange to privately publish his racy memoir. He published four volumes from 1922 to 1927. For 40 years, it was banned in Britain and the United States. However, in Paris, it once sold for a much as $100. In 1931, notorious Obelisk Press in Paris (the same one that later published risque volumes by Henry Miller and Anaïs Nin) produced a four-volume edition of Harris' memoir.