Wearable piezoresistive sensors have shown enormous application prospects in flexible electronics and human–machine interfaces. However, current piezoresistive sensors suffer from common deficiencies including high fabrication cost, poor comfort and low attachment fastness of conductive substances on substrates, thereby impeding their large-scale production and practical use. Herein, a three-dimensional all-fabric piezoresistive sensor is reported based on coating multi-wall carbon nanotubes (MWCNTs) on bicomponent nonwovens composed of core-sheath fibers. The combination of core-sheath fibers with a heat-induced welding strategy greatly improves the adhesion fastness and stability of MWCNT network. The multi-layered all-fabric structure provides as-prepared sensors with high sensitivity (9.43% kPa-1 in 0–10 kPa and 0.076% kPa-1 in 20–120 kPa), wide pressure-sensing range (0–120 kPa), fast response/relaxation time (100 and 60 ms), good reproducibility and air permeability. Application of the sensor is demonstrated through the detection of human activities (such as pulse, cough and joint movements) and the wireless monitoring of forefinger bending. Moreover, our sensor is fabricated out of cost-effective materials, using scalable approach without using glue or binders. The method established in this work may provide an efficient strategy for the design and production of high-performance all-fabric piezoresistive sensors.