The connection between the microbiome in the gut and the brain is known as the gut-brain axis and may have implications in the development and treatment of brain disorders. This narrative review paper aimed to summarise the gut-brain axis and studies surrounding the use of gut microbiota in treatment for brain disorders. The authors first highlighted that the gut microbiota is individual and varies depending on the age of the host, with full development around the age of 3 years old. Diet, infections, the use of antibiotics and stress can all affect the gut-microbiota in what is termed dysbiosis. Studies in animals indicate that the gut-brain axis may be bidirectional with either aspect affecting the other. Stress may cause dysbiosis, affecting both digestion and the immune system. In turn the gut microbiota may affect the brain through the immune system, modulation of nerves, and through the production of signalling molecules. Several diseases of the brain may be influenced by the gut microbiota. Mood disorders, brain degeneration and childhood brain development disorders were all highlighted as having potential relationships with dysbiosis. The use of probiotics in chronic fatigue syndrome, schizophrenia, brain function and autism spectrum disorder were reviewed with positive results in chronic fatigue syndrome and brain function, however studies are lacking. It was concluded that gut microbiota may directly or indirectly affect brain disorders, however the role of probiotics as a treatment needs more research. This study could be used by healthcare professionals to understand the potential role of the gut microbiota in brain disorders.