Novel cellulose-derived hybrid carbon nanofibre (CNF)/carbon nanotubes (CNTs) electrode-based structural supercapacitors, combined with a solid electrolyte, have been produced. Galvanostatic charge/discharge and electrochemical impedance spectroscopy measurements were used to assess the electrodes’ performance. The CNF/CNTs electrodes have a better capacitive performance than the plain CNF electrodes; 0.91 ± 0.02 and 3.35 ± 0.05 mF cm−2 for CNF and CNF/CNTs, respectively. A Raman spectroscopic approach was used to investigate the stress transfer properties of the CNF within a poly(methyl methacrylate) (PMMA) resin matrix. Deformation of the carbon structures was observed via shifts towards a lower wavenumber position of the G band (~ 1590 cm−1) for CNF and CNF/CNTs samples processed at a carbonization temperature of 2000 °C. Moduli of these fibres were estimated to be ~ 145 and ~ 271 GPa, respectively, suggesting the growth of CNTs not only enhances the capacitive performance but also the mechanical performance of the structural supercapacitors.