The lack of high-performance electrode materials is the main factor restricting the breakthrough of capacitive applications. Recently, integrating the advantages of different pore structures to optimize the material’s performance has led to great interest in the design of hierarchical porous carbon (HPC). Renewable, economical, and widely available kelp was selected as the carbon source to obtain a mesoporous structure using its naturally contained salts (Ca, Na, and so on) as template in this work. Subsequent chemical activation was used to get multimodal pores, and enrich the micropore structure. The micropores increase the specific surface area and provided abundant available adsorption sites, while mesopores improve not only the ionic conductivity but also the wettability of the material which is crucial in electrochemically related applications. When assembled in a pouch cell (capacitor), HPC showed a high specific capacitance of 190 F g–1 (1 A g–1, 1 mol L−1 TEABF4/AN) with a broad operation voltage range (0–2.7 V). Further applied to electric double-layer based capacitive deionization (CDI), it exhibited excellent salt removing capacity (27.2 mg g–1) with rapid response and efficient circularity. These excellent properties mainly result from its high surface area (2613.7 m2 g–1) and unique multimodal porous structure. We also verified the superior performance of a HPC material assembled CDI device driven by a pouch cell for energy-integrated applications.