The present work focuses on Annona muricata leaf extract–mediated green synthesis of pure and nickel‐doped tin oxide nanoparticles for 3%, 5% and 7% concentrations. The properties of the obtained nanoparticles were investigated through XRD, FTIR, XPS, HRTEM–SAED, SEM–EDX and UV–visible spectroscopy techniques. The XRD pattern reveals all samples have tetragonal structures with high crystallinity. The Sn–O stretching vibration has been confirmed through FTIR spectra. The XPS results demonstrate that Sn0.93Ni0.07O2 nanoparticles have Sn3d, Ni2p and O1s oxidation states. EDX spectra contain Ni, Sn and O elements, which indicate the purity of the samples. UV–visible absorption spectrum shows decreases in optical energy bandgap with increases in nickel dopant concentration. The samples exhibit notable antibacterial activity against P. aeruginosa and S. aureus. Also, Sn0.93Ni0.07O2 nanoparticle has higher antifungal activity against A. niger than against C. albicans. Moreover, SnO2 nanoparticles have considerable antioxidant activity in DPPH scavenging compared to Sn0.93Ni0.07O2 nanoparticles. Furthermore, SnO2 nanoparticles have a better cytotoxic effect for L929 normal fibroblast cell lines with an LD50 value of 146.42 μg/mL. Additionally, the photocatalytic activity of SnO2 and Sn0.93Ni0.07O2 nanoparticles was done against methylene blue dye under direct sunlight irradiation. Overall, environmentally friendly synthetic pure and Ni‐doped SnO2 nanoparticles can be used in wastewater filter technologies as well as in medical aids due to their better cytotoxic, antioxidant and antimicrobial effects.