Ni-incorporated MgFe2O4(Mg0.5Ni0.5Fe2O4) porous nanofibers were synthesized using the sol–gel electrospinning method. The optical bandgap, magnetic parameters, and electrochemical capacitive behaviors of the prepared sample were compared with pristine electrospun MgFe2O4and NiFe2O4based on structural and morphological properties. XRD analysis affirmed the cubic spinel structure of samples and their crystallite size is evaluated to be less than 25 nm using the Williamson–Hall equation. FESEM images demonstrated interesting nanobelts, nanotubes, and caterpillar-like fibers for electrospun MgFe2O4, NiFe2O4, and Mg0.5Ni0.5Fe2O4, respectively. Diffuse reflectance spectroscopy revealed that Mg0.5Ni0.5Fe2O4porous nanofibers possess the band gap (1.85 eV) between the calculated value for MgFe2O4nanobelts and NiFe2O4nanotubes due to alloying effects. The VSM analysis revealed that the saturation magnetization and coercivity of MgFe2O4nanobelts were enhanced by Ni2+incorporation. The electrochemical properties of samples coated on nickel foam (NF) were tested by CV, GCD, and EIS analysis in a 3 M KOH electrolyte. The Mg0.5Ni0.5Fe2O4@Ni electrode disclosed the highest specific capacitance of 647 F g−1at 1 A g−1owing to the synergistic effects of multiple valence states, exceptional porous morphology, and lowest charge transfer resistance. The Mg0.5Ni0.5Fe2O4porous fibers showed superior capacitance retention of 91% after 3000 cycles at 10 A g−1and notable Coulombic efficiency of 97%. Moreover, the Mg0.5Ni0.5Fe2O4//Activated carbon asymmetric supercapacitor divulged a good energy density of 83 W h Kg−1at a power density of 700 W Kg−1.