In this present investigation, plant-mediated synthesis of titanium oxide (TiO2) nanoparticles was synthesized from seagrass (Thalassia hemprichi) using the hot plate combustion method (HPCM). Synthesized TiO2 nanoparticles optical, functional, structural, and morphology properties were analyzed by UV-visible spectroscopy, Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). SEM analysis confirmed the spherical shape of the TiO2 nanoparticles were observed in various sizes, viz., 50 nm and 78 nm. The XRD analysis revealed that TiO2 nanoparticles have a body-centred cubic structure without a secondary phase. Green synthesized TiO2 nanoparticle applications were studied against the antimicrobial, antioxidant, anticancer, and photocatalytic activity. The pathogenic bacterial strains, including Staphylococcus epidermidis, Staphylococcus aureus, Klebsiella pneumonia, and Pseudomonas aeruginosa, were tested against TiO2 nanoparticles; the maximum level of activity was seen at a concentration of 50 mu g/mL. The antioxidant assays were performed against TiO2 nanoparticles, and inhibitory concentration values (IC50) were 40.28 mu g/mL of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, 52.04 mu g/mL of the acrylamide tertiary butyl sulfonic acid (ATBS) assay, and 16.91 mu g/mL of the metal chelating assay. The anticancer activity was analyzed against MCF-7 cancer cells using TiO2 nanoparticles, and the IC50 value showed 64.14 mu g/mL concentration. An eco-friendly and convenient method was formulated for the production of titanium oxide nanoparticles utilizing seagrass extract. The potential employment of TiO2 involves water treatment, biomedicine, biosensors, and nanotechnology.