This study aimed to optimize ultrasound-assisted extraction conditions for polyphenols from green tea using response surface methodology (RSM). A Box–Behnken design evaluated the effects of solvent concentration, solvent/solid ratio, extraction time, sonication power, and solvent type (ethanol, methanol, acetone) on total polyphenol content (TPC). Optimal conditions for ethanol extraction yielded the highest TPC (471.98 ± 5.33 mg GAE/g dried extract) at 60% ethanol, 50 mL/g ratio, 60 min extraction time, and 50% sonication power. The antioxidant activity of the extracts was assessed using DPPH, FRAP, and ABTS assays. Ethanol extracts exhibited the lowest IC50 values in the DPPH assay (38.386 ± 1.263 µg DE/mL), indicating the most effective radical scavenging activity, followed by methanol and acetone extracts. In the FRAP assay, acetone extracts had the lowest IC50 value (69.472 ± 1.028 µg DE/mL), while methanol extracts showed the highest antioxidant activity in the ABTS assay (IC50 45.307 ± 1.121 µg DE/mL). All extracts outperformed the standard antioxidant Trolox in these assays. Additionally, the green tea extracts demonstrated significant inhibition of α-amylase and α-glucosidase enzymes, which are associated with metabolic disorders. Ethanol extracts showed the highest inhibitory activity against α-amylase (IC50 286.362 ± 4.789 µg DE/mL) and methanol extracts against α-glucosidase (IC50 322.194 ± 0.894 µg DE/mL), both surpassing the positive control acarbose. These results underscore the efficiency of RSM in optimizing green tea polyphenol extraction and highlight the potent antioxidant and enzyme inhibitory activities of the extracts, suggesting their potential applications in managing oxidative stress and metabolic disorders.