Growing evidence has linked both the onset and symptoms of various mental disorders to lifestyle factors such as diet, exercise and sleep. The link between diet and mental health in particular in depressive disorders has gained interest in recent years. Previous reviews assessing the link between the Mediterranean diet (MedDiet) and mental health predominantly focused on depression, whilst others failed to integrate a summary of possible underlying mechanisms related to a link between MedDiet and mental health to complement their findings. In the present review, we provide a comprehensive synthesis of evidence on the MedDiet and diverse mental health outcomes complemented by narration of potential mechanisms involved. A literature search was conducted across MEDLINE, PsycINFO, Scopus, Cochrane library, Google scholar, CINAHL and Embase database. A total of 10,249 articles were found through the primary literature search and 104 articles (88 observational and 16 interventional studies) were eligible for inclusion. The Mediterranean diet (MedDiet) has been associated with favourable mental health outcomes in adult populations, including reduced depressive and anxiety symptoms, lower perceived stress, and improved quality of life and overall well-being, both in healthy individuals and those with comorbidities, across diverse geographical settings. Mechanisms involved include anti-oxidant, anti-inflammatory potential of MedDiet and its effect on gut microbiota. Further research is warranted to rigorously establish causal inferences and to guide the optimal incorporation of Mediterranean diet principles into comprehensive prevention and treatment strategies aimed at improving mental health outcomes.