Modern diagnosis of various forms of malignant brain tumours (gliomas) is primarily carried out by imaging methods, such as magnetic resonance imaging, electroencephalography, and positron emission tomography; brain biopsy is also used. The disadvantages of these methods are their inaccuracy and invasiveness, which entails certain risks for the patient’s health. Therefore, finding more reliable and safe methods for diagnosing gliomas, including their biomarkers in the blood and cerebrospinal fluid, is an urgent task. This review aimed to collect data on potential biomarkers of malignant brain tumours in body fluids, in particular, cerebrospinal fluid and blood, discovered so far and having diagnostic value. The information was searched for in the following databases: UpToDate, eLibrary, PubMed, Medline, and Scopus, as well as in the search engines Google Scholar and Web of Science. Materials from the website of the World Health Organization were also used. The review mainly included articles written over the past 5 years. We found information on such biomarkers as miRNA-15b and miRNA-125b, proline, YKL-40 glycoprotein, circDNA (circular DNA) and circRNA (circular RNA), extracellular vesicles, fatty acids, and fatty acid synthases. The authors conclude that the following biomarkers: YKL-40, circDNA, circRNA, and extracellular vesicles have a large evidence base and can already be used in clinical practice. Other biomarkers require more detailed and extensive studies.