Duff was born in Waitahuna Gully, a gold mining town in Otago. He received his tertiary education at Otago and Canterbury Universities. At the age of 18 he volunteered for the South African war and on his return he won a scholarship to study for the Presbyterian ministry from the Synod of Otago and Southland. Influenced by writers such as Emerson and Thoreau he dropped out and became a journalist. He worked on a number of papers including the "Sun" in Christchurch, "The Timaru Herald" (as editor), "The Press" in Christchurch, as editorial assistant (under Michael Cormac Keane) then editor. At "The Press" he worked with writers such as Ngaio Marsh, M. H. Holcroft and Walter D'Arcy Cresswell. He resigned over his coverage of the Christchurch tramway strike, which the owners thought too sympathetic to the unions.