The hazardous heavy metal ion Cr(VI) is harmful and easily mobile in the environment. Cr(VI) poisoning can cause delayed seed germination and damaged plant growth. This study suggested a green and simple synthesis method of ZnO microparticles (ZnO MPs) from Zn(CH3COO)2 solution and aqueous leaf extract of Dolichandrone spathacea (L. f.) K. Schum for protecting the legume plant (Vigna radiata) against the Cr(VI) stress. The optimized conditions for the synthesis of these MPs were determined using computational and experimental approaches. The characterization of ZnO MPs was analyzed by surface morphology, particle sizes, and elemental components using modern methods. The Zn MPs successfully exhibited the potential protective effects on the seed germination and seedling vigor of V. radiata under Cr(VI) stress. The results of PPR and ABTS assays also indicated that the antioxidant capacity of non-enzymatic antioxidants from leaves under Cr(VI) stress significantly reduced (46.83 ± 1.938% and 69.60 ± 2.17%, respectively) as compared to supplement of ZnO-MPs increased (55.44 ± 2.624% and 78.07 ± 0.820%, respectively). This study is an essential report for the agricultural field, which can apply further the new and green zinc-micronutrient fertilizer to mitigate the adverse effects of heavy metal contamination on crop cultivation.