We report the effect of Sr²⁺ and Mn³⁺ co-doping BiFeO₃ on the crystal structure and the multiferroic properties of Bi_0.95Sr_0.05Fe_1-xMn_xO₃ (0.0 = x ≤ 0.4, Δx = 0.1) powders, synthesized by assisted high-energy ball milling of stoichiometric mixtures of Bi₂O₃, Fe₂O₃, SrO, and Mn₂O₃; the powders were pressed at 900 MPa and sintered at 800 °C. X-ray diffraction and Rietveld refinement reveal the effect of Sr²⁺ and Mn³⁺ on the crystal structure. These elements act as inhibitors of secondary phases. Magnetic behavior, obtained using vibrating sample magnetometry shows antiferromagnetic order and an increase in magnetic susceptibility, due to slight differences in ionic radii and low crystal structure distortion. All the samples show high relative permittivity values, which is augmented by doping with Sr²⁺ and Mn³⁺ ions furthermore, the doping increases dielectric dissipation factor; it is attributed to their interaction with different oxidation state cations like Fe³⁺, Fe²⁺, Mn³⁺, Mn²⁺, Bi³⁺, and Sr²⁺, into the crystal structure of BiFeO₃. Additionally, it was found increments of the electrical conductivity, due to the domain-wall charge accumulation phenomenon. In the same way, the relative permittivity improves as an effect of domain-walls conductivity, induced by Sr and Mn co-doping. The magnetodielectric effect presents a change in mechanism origin, from core-dominated (grain) to interface-dominated (electrode-dielectric, and grain-grain boundary), as a result of domain-wall charge accumulation.