Flexible electrochemical supercapacitors have shown great potential in the next-generation wearable and implantable energy-storage devices. Conductive polymer hydrogels usually possess unique porosity, high conductivity, and broadly tunable properties through molecular designs and structural regulations, thus holding tremendous promise as high-performance electrodes and electrolytes for flexible electrochemical supercapacitors. Numerous chemical and structural designs have provided unlimited opportunities to tune the properties of conductive polymer hydrogels to match the various practical demands. Various electrically and ionically conductive hydrogels have been developed to fabricate novel electrodes and electrolytes with satisfactory mechanical and electrochemical performance. This feature article focuses on the fabrication and applications of conductive polymer hydrogel composites and nanocomposites as respective electrodes and electrolytes for flexible electrochemical supercapacitors. First, we introduce the representative strategies to prepare electrically and ionically conductive polymer hydrogels. Second, conductive polymer hydrogel composites and nanocomposites as supercapacitor electrodes and electrolytes are presented and discussed. Finally, challenges and perspectives on conductive polymer hydrogel composites and nanocomposites for future flexible electrochemical supercapacitors are presented.