The son of a car repairman, Towell grew up in a large family in rural Ontario, Canada. During studies in visual arts at Toronto's York University, he was given a camera and taught how to process black and white film. A stint of volunteer work in Calcutta in 1976 provoked Towell to photograph and write. In 1984, he became a freelance photographer and writer focusing on the dispossessed, exile and peasant rebellion. He completed projects on the Nicaraguan Contra war, on the relatives of the disappeared in Guatemala, and on American Vietnam War veterans who had returned to Vietnam to rebuild the country. His first published magazine essay, Paradise Lost, exposed the ecological consequences of the catastrophic Exxon Valdez oil spill in Alaska's Prince William Sound. He became a Magnum nominee in 1988 and a full member in 1993. In 1996, Towell completed a project based on ten years of reportage in El Salvador, followed the next year by a major book, Then Palestine. His fascination with landlessness also led him to the Mennonite migrant workers of Mexico, an eleven-year project completed in 2000.