The coveted award honouring achievements in medical research opened this year's series of prize announcements.
It will be followed by prizes for physics, chemistry, literature, peace and economics.
"Warren, a pathologist from Perth, Australia, observed small curved bacteria colonising the lower part of the stomach in about 50% of patients from which biopsies had been taken," the Nobel Assembly said.
"He made the crucial observation that signs of inflammation were always present in the gastric mucosa close to where the bacteria were seen."
Marshall became interested in Warren's findings and together they initiated a study of biopsies from 100 patients.
"After several attempts, Marshall succeeded in cultivating a hitherto unknown bacterial species - later denoted Helicobacter pylori - from several of these biopsies," the assembly said.
"Together they found that the organism was present in almost all patients with gastric inflammation, duodenal ulcer or gastric ulcer. Based on these results, they proposed that Helicobacter pylori is involved in the aetiology (cause) of these diseases."
The pair used common technology such as fibre endoscopy, to help determine that Helicobacter pylori was responsible for many stomach ulcers.
Marshall (R) and Warren (L)
examined 100 biopsies
"Thanks to the pioneering discovery by Marshall and Warren, peptic ulcer disease is no longer a chronic, frequently disabling condition, but a disease that can be cured by a short regimen of antibiotics and acid secretion inhibitors," the assembly said.
By culturing the bacteria, they were able to make studying it and the illnesses, easier.
"In 1982, when this bacterium was discovered by Marshall and Warren, stress and lifestyle were considered the major causes of peptic ulcer disease," the assembly said in its citation.
"It is now firmly established that Helicobacter pylori causes more than 90% of duodenal ulcers and up to 80% of gastric ulcers."
The medicine prize is awarded by the Karolinska institute in Stockholm as stated in the will of Alfred Nobel, a Swedish industrialist who founded the prestigious awards in 1895.
"Thanks to the pioneering discovery by Marshall and Warren, peptic ulcer disease is no longer a chronic, frequently disabling condition, but a disease that can be cured by a short regimen of antibiotics and acid secretion inhibitors"
The process for selecting winners is extremely secretive - nominations are kept sealed for 50 years - leaving Nobel-watchers little to go on in their speculation.
The medicine prize includes a cheque for 10 million kronor ($1.3 million), a diploma, gold medal and a handshake with the king of Sweden at the award ceremony in Stockholm on 10 December.
Last year's laureates, Americans Richard Axel and Linda Buck, won for discovering how people can recognise an estimated 10,000 odours - from spoiled meat to a lover's perfume - and remember it.