The olive tree (Olea europaea L.) is one of the most widespread and cultivated trees in the Mediterranean region. The crop faces many challenges in the context of climate change, particularly frequent droughts due to inter-annual variability in the rainfall. Such a situation leads to the emergence of more arid areas, raising questions about the sustainability of the olive crop in the Mediterranean region. Therefore, a deeper knowledge of the mechanisms of drought resilience is crucial for predicting the response of trees to climate change. Objectives: The analysis of the functional and structural leaf-based traits of olive trees can be an effective strategy to (i) classify the current cultivars based on their adaptability to future climatic challenges and (ii) identify the most relevant and easily measurable traits for use in breeding programmes. Methods: A total of 80 olive cultivars were selected from the World Olive Germplasm Bank of Meknes (INRA, Morocco); each cultivar was represented by two trees, and six leaves were taken from each tree. Twelve traits were measured from each leaf, and these twelve traits were divided into three groups: (1) morphological traits, represented by the leaf area (LA), leaf length (LL), leaf width (LW) and leaf shape (LL/LW); (2) ecophysiological traits such as the stomatal density (DS), trichome density (DT) and leaf blade thickness (LT); and (3) structural traits, represented by the dry and fresh leaf weights (DM and FM), leaf mass per area (LMA), specific leaf area (SLA) and leaf dry matter content (LDMAC). The results of an ANOVA and the determination of the coefficient of variation showed that high phenotypic variability was observed for all the traits studied. In addition, the ANOVA showed that all the measured traits can be used for early detection of stress-tolerant varieties, especially the leaf length (LL), leaf shape (LL/LW), leaf thickness (LT) and leaf dry and fresh weights (DM and FM). In addition, investigation of leaves' morphological and structural traits can be used as a simple and rapid way to classify varieties with respect to their response to drought. Furthermore, the European varieties, such as Cobrancosa, Koroneiki, Arbequina and others, were the most stress-tolerant varieties. Conclusions: There was significant variation in the leaves' functional traits among the olive cultivars, with the variability depending on the type of trait and cultivar origin. This suggests that specific traits can be used to identify drought-tolerant cultivars. All the traits can be used in breeding programmes for variety selection, but the leaf shape, leaf width, leaf thickness and dry and fresh weights are the traits that show the most phenotypic variability between varieties. In future, phenotypic plasticity studies could be extended to other local and introduced varieties for comparison with those covered in this study.