<p>Multiferroic nanoparticles are extensively studied as they exhibit ferroelectricity, ferromagnetism and ferro-elasticity in a single-phase material. These nanoparticles play an important role in multifunctional and eco-friendly devices. The present manuscript deals with the synthesis of manganese (Mn) doped bismuth ferrite (Bi_1-xMn_xFeO₃) nanoparticles at 0 ≤ <i>x</i> ≤ 0.1 using a sol-gel auto combustion method. The role of manganese (Mn) concentration on structural, optical, magnetic and dielectric properties was investigated. More importantly, the role of Mn concentration on visible light photocatalytic application was explained in detail. The XRD results confirmed the rhombohedral (0 ≤ <i>x</i> ≤ 0.07) and tetragonal structures (<i>x</i> ≥ 0.1) of Bi_1-xMn_xFeO₃ nanoparticles. The Bi_1-xMn_xFeO₃ nanoparticles exhibited high optical response (absorbance) in the visible region which increased with increasing Mn concentration. A decrease in optical band gap (E_g) was noted from 2.1 eV to 1.36 eV with increasing Mn concentration (0 ≤ <i>x</i> ≤ 0.10). The magnetic properties were studied at room temperature (300 K) by applying an external magnetic field of ±15 kOe. The Bi_1-xMn_xFeO₃ nanoparticles exhibited paramagnetic (0 ≤ <i>x</i> ≤ 0.05) and ferromagnetic (<i>x</i> &gt; 0.05) behaviours with increasing Mn concentration. Dielectric measurements were carried out at room temperature by varying frequency. An increase in dielectric loss was observed with increasing Mn concentration. The visible light photo catalytic activity of Bi_1-xMn_xFeO₃ nanoparticles was investigated using Rhodamine B dye and enhanced photo catalytic degradation activity was observed with increase of Mn concentration.</p> Graphical Abstract <p></p>