The importance of singlet oxygen (¹O₂) in the environmental and biomedical fields has motivated research for effective ¹O₂ production. Electrocatalytic processes hold great potential for highly-automated and scalable ¹O₂ synthesis, but they are energy- and chemical-intensive. Herein, we present a Janus electrocatalytic membrane realizing ultra-efficient ¹O₂ production (6.9 mmol per m³ of permeate) and very low energy consumption (13.3 Wh per m³ of permeate) via a fast, flow-through electro-filtration process without the addition of chemical precursors. We confirm that a superoxide-mediated chain reaction, initiated by electrocatalytic oxygen reduction on the cathodic membrane side and subsequently terminated by H₂O₂ oxidation on the anodic membrane side, is crucial for ¹O₂ generation. We further demonstrate that the high ¹O₂ production efficiency is mainly attributable to the enhanced mass and charge transfer imparted by nano- and micro-confinement effects within the porous membrane structure. Our findings highlight a new electro-filtration strategy and an innovative reactive membrane design for synthesizing ¹O₂ for a broad range of potential applications including environmental remediation.