This research article presents the synthesis of MnWO₄ nanoparticles using a combination of MnCl₂ and Na₂WO₄·2H₂O as precursors, with water as the sole solvent for dissolution, eliminating the need for additional solvents. The synthesized materials underwent comprehensive characterization employing various analytical techniques, including X-ray diffraction, scanning electron microscopy, UV–visible spectrophotometry, and Fourier Transform Infrared Spectrometry. The photocatalytic activity of MnWO₄ nanoparticles for degrading the organic contaminant methylene blue in water was also investigated under visible light irradiation. Notably, a significant degradation of methylene blue was observed, with 98% degradation achieved within a 120-min irradiation period. Additionally, the material was subjected to electrochemical studies to assess its sensing capabilities and exhibited strong sensing activity by detecting nano-molar concentrations of nitrite solution.