He received his MBBS degree from the University of Adelaide, having completed his high school education at St Peter's College, Adelaide. In 1967 he was became a member the Royal College of Pathologists of Australia and became a senior pathologist at the Royal Perth Hospital where he spent most of his career. At the University of Western Australia with Barry J. Marshall, Warren proved that the bacterium is the cause of stomach ulcers. Warren helped develop an easy diagnostic test (C-urea breath-test) for finding "H. pylori" in ulcer patients. In 2005, Warren and Marshall were awarded the Nobel Prize in Medicine.