In this work, direct carbonization of polyaniline manganese ferrite (Mn-PANI) nanocomposite was employed to prepare a novel N-doped carbon material decorated with manganese ferrite (Mn-CPANI) and implemented as an ultra-stable symmetric supercapacitor electrode material. The surface morphology of as-prepared samples is investigated with field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Also, uniform distribution of manganese ferrite (MnFe2O4) on PANI surface and the N-doped carbon material is confirmed through EDX analysis. Carbonized nanocomposite contains about 8 wt% of nitrogen. The obtained Mn-CPANI nanocomposite shows a high specific capacitance of 329 F g−1 and exhibits excellent capacitance retention of 83.2% from 1 to 10 A g−1, which is more stable compared to Mn-PANI nanocomposite. Moreover, the symmetric Mn-CPANI supercapacitor cell possesses a specific capacitance of about 246 F g−1 (at 1 A g−1) and an excellent stable cyclability (only 3% of specific capacitance decreases after 10000 cycles). The excellent enhanced electrochemical performance of Mn-CPANI nanocomposite could be originated from the combination and synergism of N-doped carbon material as an electrical double-layer capacitor with pseudocapacitive MnFe2O4. As a result, a novel electrode material is developed for high-performance ultra-stable energy storage devices.