This work aimed to establish the content of phenolic compounds, carbohydrates, and organic acids and to determine their potential to inactivate α-amylase, α-glucosidase, pancreatic lipase, 15-lipoxygenase (15-LOX), acetylcholinesterase (AChE), and butyrylcholinesterase (BuChE), and antioxidant activity (ABTSo+ and FRAP) in 43 Prunus domestica cultivars. We identified 20 phenolic compounds, including, in the order of abundance, polymeric procyanidins, flavan-3-ols, phenolic acids, flavonols, and anthocyanins. The total content of phenolic compounds varied depending on the cultivar and ranged from 343.75 to 1419 mg/100 g d.w. The cultivars of Ś2, Ś11, and Ś16 accumulated the greatest amounts of polyphenols, while in cvs. Ś42, Ś35, and Ś20 polyphenols were the least abundant. The highest antioxidant potential of 7.71 (ABTSo+) and 13.28 (FRAP) mmoL Trolox/100 g d.w. was confirmed for cv. Ś11. P. domestica fruits showed inhibitory activity toward α-amylase (2.63–61.53), α-glucosidase (0.19–24.07), pancreatic lipase (0.50–8.20), and lipoxygenase (15-LOX; 4.19–32.67), expressed as IC50 (mg/mL). The anti-AChE effect was stronger than the anti-BuChE one. Cv. Ś3 did not inhibit AChE activity, while cv. Ś35 did not inhibit BuChE. Thanks to the abundance of biologically active compounds, P. domestica offers several health-promoting benefits and may prevent many diseases. For these reasons, they are worth introducing into a daily diet.