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Background: The biosynthesis of zinc oxide nanoparticles (ZnO NPs) has received increasing attention in the field of nanotechnology due to their biomedical applications. With this aim, the present study was performed to synthesize biocompatible ZnO NPs using stems, leaves, and inflorescences extracts of the Tephrosia purpurea (T. purpurea) and Heliotropium indicum (H. indicum) medicinal plants. Objective: The objective of this study was to synthesize ZnO NPs from T. purpurea and H. indicum and determine their ability as an alternative for toxic synthetic antioxidants. Methods: The preliminary phytochemical screening of T. purpurea and H. indicum and quantitative determination of phenols and flavonoids were carried out by using spectrophotometric methods. The antioxidant potential of ZnO NPs was assessed through 2,2–diphenyl-1-picrylhydrazyl (DPPH) and phosphomolybdenum assays against butylated hydroxytoluene standard. Results: Qualitative phytochemical analysis of plant extracts confirmed the presence of terpenoids, alkaloids, carbohydrates, tannins, phenols, flavonoids, and proteins. The highest percentage of phenolics (88.3 ± 1.7 mg GAE/g) and flavonoids (727.1 ± 103.5 mg QE/g) was recorded for H. indicum inflorescences and T. purpurea stems. The T. purpurea stems mediated ZnO NPs showed the most potent DPPH radical scavenging capacity of 81.53 ± 0.14% with an IC50 value of 152.38 ± 0.70 μg/mL, while ZnO NPs synthesized using H. indicum inflorescences and T. purpurea stems indicated the highest total antioxidant capacity of 94.71 ± 2.50 and 91.34 ± 1.07%, respectively. Conclusion: The obtained results revealed the significance of T. purpurea and H. indicum as effective stabilizing agents to develop surface protective ZnO NPs, which can be used as promising antioxidants in the biological systems.