Tin dioxide (SnO2) and Ni-doped SnO2 (Ni–SnO2) NPs were successfully obtained via a cost effective, phytogenic and green method using aqueous leaf extract of Tradescantia spathacea. With the incorporation of Ni2+ into SnO2 lattice, the structural and optical properties along with surface morphologies of the SnO2 NPs were affected. The crystallite size obtained from powder X-ray diffraction was between 13 and 17 nm. X-ray photoelectron spectroscopy analysis further confirmed the synthesis of the SnO2 and Ni–SnO2 NPs and the density of states was proposed accordingly using the valence band-XPS data. The optical studies of the synthesized materials using photoluminescence (PL) was also conducted where increased Ni doping resulted in a decreased PL intensity. The UV–Vis absorbance of SnO2 and Ni–SnO2 NPs was red-shifted and achieved band gap energies between 2.67 and 2.83 eV. Photoantioxidant activity was carried out using DPPH assay method in the dark and under visible light irradiation. Enhancement of the photoantioxidant activity for SnO2 and Ni–SnO2 NPs was observed under visible light illumination.