Mn-doped cobalt ferrite nanoparticles were synthesized via the green route combustion-assisted method using tamarind seed powder as a fuel with the chemical formula MnxCo1-xFe2O4, where x = 0.0, 0.2, 0.4, and 0.6, and named as CF, MCF-1, MCF-2, and MCF-3 NPs, respectively. XRD, FT-IR, SEM with EDS, XPS, TEM, CV, PL, and UV–visible spectroscopy have been employed to characterize the synthesized nanoparticles. The average crystalline sizes of NPs were 5.7, 6.1, 6.8, and 7.6 nm, and the lattice parameters increases as the manganese dopant level rises, owing to the XRD patterns. FT-IR spectra verified the observation of the metal-oxygen bond's vibrational stretching frequency in the tetrahedral and octahedral lattices. Using X-ray photoelectron spectroscopy, the elemental composition, oxidation state, and transition state of the synthesized nanoparticles were identified. The structure resembles nanoflakes with agglomeration, as revealed by SEM and HRTEM, and the elemental composition was verified by EDS. UV–visible spectroscopy was employed to figure out the bandgap, which decreases as the level of manganese doping rises. As the dose of manganese dopant was increased, the peak intensity of the luminescence spectra reduces. Synthesized NPs showed good electrochemical behaviour in CV studies. Under visible light illumination, the photocatalytic efficacy of synthesized nanoparticles was evaluated with methylene blue dye.