Duncan Macmillan (born 1980) is an English playwright and director. He is most noted for his plays Lungs, People, Places and Things, Every Brilliant Thing and the stage adaptation of the George Orwell novel Nineteen Eighty-Four which he co-adapted and co-directed with Robert Icke. Macmillan's play Lungs had a major revival at the Old Vic Theatre in 2019, starring Matt Smith and Claire Foy. Macmillan co-created and wrote the 2020 BBC television drama series Trigonometry with Effie Woods.