Oxygen (O) functionalized carbon materials can provide high charge storage because of their enrichment in redox-active sites, but they do not display fast charge transfer kinetics, which is caused by the loss of electrical conductivity from the disruption of sp2 carbon networks. To address this challenge, we develop a novel two-step protonic acid catalysis method that partially re-establishes a π-π conjugated system for engineering fast electronic transport channels in an O-functionalized carbon textile. This method largely maintains the sp2 carbon network integrity with abundant active O-functional groups embedded into a graphitic carbon host. The resultant functionalized carbon textile features both high O-content and high electrical conductivity. When incorporated in flexible electrodes for supercapacitors, the material exhibits ultrahigh areal capacitance of 2580 mF cm−2 and excellent rate performance, outperforming other reported carbon-based flexible electrodes. The constructed flexible supercapacitor also delivers excellent electrochemical performance and mechanical stability under flexible deformations. Such a system might shed light on the design of O-functionalized carbon materials with both high O-content and high electrical conductivity for energy storage/conversion.