Ageing is a multifactorial process associated with reduced function and increased risk of morbidity and mortality. Recently, nine cellular and molecular hallmarks of ageing have been identified, which characterise the ageing process, and collectively, may be key determinants of the ageing trajectory. These include genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion and altered intercellular communication. Healthier dietary patterns reduce the risk of age-related diseases and increase longevity and may influence positively one or more of these hallmarks. The Mediterranean dietary pattern (MedDiet) is a plant-based eating pattern that was typical of countries such as Greece, Spain, and Italy pre-globalisation of the food system and which is associated with better health during ageing. Here we review the potential effects of a MedDiet on each of the nine hallmarks of ageing, and provide evidence that the MedDiet as a whole, or individual elements of this dietary pattern, may influence each hallmark positively—effects which may contribute to the beneficial effects of this dietary pattern on age-related disease risk and longevity. We also highlight potential avenues for future research.