This study analysed the phytochemical composition and antioxidant activity of Piper betle leaves and Piper nigrum seeds extracted using solvents of varying polarity: hydroethanol, ethanol–hexane, and methanol. Quantitative analysis revealed marked differences in phenolic, flavonoid, and terpene contents among the extracts. The hydroethanolic extract of P. betle (B1) exhibited the highest concentrations of phenols (787.08 ± 59.32 µg/mL) and flavonoids (576.04 ± 23.56 µg/mL), whereas the ethanol–hexane extract of P. nigrum (P2) contained the highest terpene level (1027.69 ± 38.77 µg/mL). These findings highlight the superior efficiency of polar solvents for extracting phenolic and flavonoid compounds from P. betle, while non-polar systems favoured terpene recovery from P. nigrum. Antioxidant activity, evaluated using the DPPH radical scavenging assay, demonstrated strong inhibition across all P. betle extracts (>91%), with the hydroethanolic extract (B1) achieving the highest scavenging activity (94.00%). In contrast, P. nigrum seed extracts showed substantially lower activity, with inhibition values between 24.22% and 24.44%, irrespective of solvent type. Overall, the comparative analysis establishes P. betle leaves as a richer source of phenolic and flavonoid constituents with robust antioxidant potential, while P. nigrum seeds predominantly contribute terpene compounds with comparatively limited radical scavenging activity. These results underscore the greater potential of P. betle for applications in functional foods, nutraceuticals, and therapeutic formulations.