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The main objective of this work was to evaluate Pistacia atlantica by analyzing the chemical composition of the methanolic extract of its leaves; determining its content of phenolic compounds, flavonoids, and condensed tannins; and finally testing its antioxidant and inhibitory activities against enzymes involved in several diseases. To identify phenolic compounds, high-performance liquid chromatography with an ultraviolet detector was used. The Folin–Ciocalteu trichloroaluminum and vanillin methods were employed to quantify phenolic compounds, flavonoids, and condensed tannins. The antioxidant effect was tested using 5 different methods. Acetylcholinesterase, butyrylcholinesterase, α-glucosidase, and tyrosinase were used to evaluate the inhibitory power of the plant against the enzymes. The results indicated the presence of phenolic compounds in the extract, including phenolic acids and flavonoids. The total content of phenolic compounds, flavonoids, and condensed tannins were, respectively, 36.089 ± 0.047 mg of gallic acid equivalents per gram, 0.775 ± 0.01 mg of quercetin equivalents per gram, and 5.44 ± 0.5 mg of catechin equivalents per gram of dry plant. High antioxidant activity was observed, with IC50 values ranging from 3.50 ± 0.05 to 11.11 ± 4.03 μg/ml, and concentrations at absorbance 0.5 ranging from 0.84 ± 0.08 to 54.57 ± 0.24 μg/ml. A strong antidiabetic effect was recorded, far exceeding the effect of acarbose, alongside notable anti-Alzheimer and anti-tyrosinase effects.