Semiconductor metal-substituted tin oxide (SnO₂) has drawn a great deal of attention due to its excellent properties. This study focuses on the photocatalytic properties of 3d transition metals, specifically manganese (Mn) and iron (Fe), emphasizing the role of unpaired electrons in enhancing photocatalytic activity. A Sn_0.99-Mn_0.05-Fe_0.05O₂ sample was synthesized by the sol–gel wet chemical precipitation method. The crystallite size and structure of doped SnO₂ were determined usinga modified Debye Scherer’s formula. Lattice constants were evaluated from peaks obtained by the X-ray diffraction (XRD) technique. The value of crystallite size estimated by Debye Scherer’s formula lies in the range 3–5 nm, indicating the nano-crystalline nature of the sample. Using transmission electron microscopy (TEM), the obtained average diameter was 3.75 nm, calculated with the help of ImageJ, which is in good agreement with the crystallite size obtained via XRD. The irregular morphology of the sample was analyzed by field emission scanning electron microscopy (FESEM). An energy dispersive X-ray (EDX) analysis confirmed the presence of elements such as tin, oxygen, manganese and iron. Fourier transform infrared (FT-IR) spectrum displayed Sn-O characteristic bands as well as inculcated metal elements. The optical and photocatalytic results were characterized using UV-Visible spectroscopy. The absorbance for pristine and intercalated samples was observed at 217 nm and 218 nm, respectively. Their optical band gaps were 3.10 eV and 2.69 eV, respectively, indicating that the band gaps narrow upon intercalation. Photoluminescence spectra were obtained in the visible spectrum range (300–600 nm) and confirmed the defects and impurity states formed due to the intercalation of Mn and Fe transition elements. The photocatalytic activity results revealed that Mn-Fe/SnO₂ has a better photocatalytic performance of methylene blue (MB) dye solutioncompared to pristine SnO₂.