While his older brother has gone on to make numerous other films, MacKinnon has chosen to travel throughout the world, living in Morocco, London and Sydney, Australia. While Down Under, he met and became romantically involved with New Zealand-born filmmaker Jane Campion. Billed as William MacKinnon, he served as producer and script editor on her debut feature "Sweetie" (1989). He also worked as script editor on her Oscar-winning screenplay for "The Piano" (1993), but by the time of its release, their personal relationship had ended. Additionally, he has produced two nonfiction films, Sue Clayton's "The Last Crop" and "Motherland." MacKinnon has long been developing the Christopher Isherwood memoir "My Guru and His Disciple" as a feature film.