Dr. Marshall was born in Kagoorlie, Western Australia, and educated in Perth. He graduated in Medicine from the University of Western Australia in 1974. After completion of his postgraduate training, he became a fellow of the Royal Australian College of Physicians (FRACP) in 1983, and held positions in General Medicxine, Microbiology, and Gastroenterology at the Royal Perth Hospital until 1986. In 1986 he joined the Division of Gastroenterology, Faculty of Medicine, University of Virginia, in Charlottesville, VA, where he is currently Clincal Associate Professor. He is also the founder and President of the Helicobacter Foundation in Charlottesville.

When he was a medical resident in 1981, Dr. Marshall and pathologist Dr. Robin Warren noticed that spiral bacteria, though not recognized as common occupants of the human gastric mucosia, were present in over half the patients attending for upper GI endoscopy. In 1982 Dr. Marshall was the chief investigator in a study that established the significance of the new bacterium in gastric ulcer and doudenal ulcer. The organism was isolated and given the name Helicobacter Pylori. Later, initially through experiments with himself as a subject, Dr. Marshall established that gastritis associated with hypochlorhydria is symptomatic of acute H. Pylori infection. Dr. Marshall was the first to appreciate the need for drugs with an antibacterial effect rather than acid-reducing drugs, to reduce the relapse rate in duodenal ulcers.