In this study, we used a spray-drying method to synthesize a hierarchically structured binary nanocomposite comprising highly porous NiO nanosheets and polyaniline:poly(sodium 4-styrenesulfonate) (PANI:PSS) materials. In this system, the porous NiO nanosheets—obtained through thermal decomposition of β-Ni(OH)2 derived from microwave-assisted hydrothermal treatment—dispersed well in the PANI:PSS solution. The homogeneous suspension was then processed through spray-drying and crosslinking of PANI:PSS and GOPS to form NiO/PANI:PSS microspheres. The PANI polymer served as a good conductor and thin spacer that prevented the NiO nanosheets from undergoing layer-to-layer stacking. Moreover, the crosslinked PANI:PSS acted as a binder that held all of the active materials together, leading to high mechanical integrity and excellent water-resistance. Through a synergistic effect in this unique nanoarchitecture, the NiO/PANI:PSS nanocomposite displayed a higher capacitance (834 F/g) at 1 A/g compared with that of NiO (380 F/g) and PANI:PSS (264.5 F/g) individually. Furthermore, the NiO/PANI:PSS composite displayed remarkable rate performance and outstanding cycling life—88.9% retention of specific capacitance after 3000 repeated charge/discharge tests—as a result of its low resistance and high (SSA). We fabricated asymmetric supercapacitors (ASCs) incorporating NiO/PANI:PSS and active carbon (AC) to further explore the capacitive performance of the composite. The as-fabricated devices also delivered remarkable performance, with an energy density of 32.84 Wh/kg, a power density of 375 W/kg, and excellent cycle life.