This research aims to design an eco-friendly approach for synthesizing green Selenium nanoparticles by mixing the leaf extract of Moringa oleifera and Sodium Selenite solution. The Selenium nanoparticles were characterized using UV-vis, FTIR, XRD and SEM, EDS, DLS, Zeta potential, and AFM. SeNPs were assessed for anti-microbial, anti-biofilm, and antioxidant assay. The analysis of X-ray diffraction reveals that Selenium NPs are 71.2 nm with a crystallinity of 66.8%. The band gap energy shows 2.4eV. Green-produced SeNPs were discovered to have high antibacterial action as well as significant antioxidant activity (IC50-50.21 μg for DPPH, 50.06 μg for ABTS, 62.9 μg for FRAP). SeNPs degrade crystal violet dye effectively when exposed to UV radiation. SeNPs were very effective against the biofilm formation by Pseudomonas aeruginosa, it was able to cease its growth to the maximum compared to the other bacterial strains. The full factorial method was followed to understand the consequences of three variable factors that is pH, time, and concentration of the SeNPs on the dye degradation. The concentration and pH were significant which influenced the dye degradation. Apart from this Selenium nanoparticles were able to influence the growth of Phaseolus vulgaris by increasing the amount of chlorophyll, tannin, flavonoid, and phenol in the plant grown in the presence of selenium compared to the control. The morphological characteristics of the plant were seen to be influenced by the selenium. Molecular analysis was also performed to study the change in the DNA content and the protein content. We conclude that SeNPs can be used by agro-based industries and textile dye industries. All rights reserved, Elsevier.