Single phase Bi1-xLaxFeO3 nanoparticles have been successfully synthesized with varied concentration (0.0 ≤ x ≤ 0.2) for the photocatalytic degradation of an industrial dye. The room temperature X-ray diffraction (XRD) pattern of La 3+ doped BiFeO3 nanoparticles reveals the structural phase transition from rhombohedral (R3c) to orthorhombic (Pnma) at x=0.1, which is further analyzed via Rietveld refinement. The La 3+ doped BiFeO3 nanoparticles have much negative enthalpy of formation (ΔHf) than undoped BiFeO3. The particle size gradually decreases from ~132 to ~68 nm with La 3+ doping. Magnetic and ferroelectric transition temperatures are found to be slightly shifted towards room temperature upto x= 0.1 and then higher temperature side which could be attribute to the particle size effect. All compositions presented weak ferromagnetic ordering, which indicates that the La 3+ substitution in the BiFeO3 matrix released the latent magnetization. The increase in the energy band gap from 2.045 to 2.658 eV with cutoff wavelengths 639.58 and 513.061 nm for x=0.0 and 0.2 respectively, increases the visible light efficiency of photocatalytic activity in La 3+ doped BiFeO3 samples. The photodegradation efficiency of La 3+ doped BiFeO3 for azo-dye RB-5 is observed to be ~27% higher as compared to the undoped BiFeO3 (43% photodegradation efficiency), which makes it suitable for visible-light responsive photocatalysis for photocatalytic applications.