Brittle fracture and facile crack initiation present significant challenges for the toughening and processing of cementitious composites. In this work, the continuous and large-scale fabrication of cement-based fiber is enabled by cellulose-assisted wet spinning strategy, during which cement grains are in-situ implanted into porous cellulose matrix. The subsequent hydration process induces the in-situ formation of a hard continuous network which interconnects with the flexible porous cellulose skeleton, leading an interpenetrating dual-network architecture formed within the resulting cellulose-supported cement-based (CSC) fibers. This architecture provides simultaneous mechanical strength and toughness. Moreover, the resulting CSC fibers exhibit hydration-enabled manufacturability and can be woven into fabrics. The CSC fiber fabric demonstrates high toughness and impact resistance, lightweight properties, low thermal conductivity, and great water-resistance, holding significant potential for applications in thermal insulation, seismic high-rise buildings, and durable construction materials.