Textile-based electronics have attracted much attention since they can perfectly combine the functionality of wearable devices with the soft and comfortable properties of flexible textile fibers. In this work, we report a dynamically stretchable high performance supercapacitor for powering of the integrated sensor in all-in-one textile system to detect various biosignals. The supercapacitor fabricated with MWCNT/MoO3 nanocomposite electrodes and non-aqueous gel electrolyte, along the course direction of the fabric exhibits stable and high electrochemical performance under dynamic and static deformation, including stretching in real time, regardless of the strain rate. The strain sensor created along the wale direction of the fabric shows a high sensitivity of 46.3 under an applied strain up to 60%, a fast response time of 50 ms, and high stability over 10,000 cycles of stretching/releasing. Finally, the supercapacitor and strain sensor are integrated into an all-in-one textile system via liquid-metal interconnections, and the sensor is powered by the stored energy in the supercapacitor. This system sewed into cloth successfully detects strain due to joint movement and the wrist pulse. This work demonstrates the high feasibility of utilizing the fabricated stretchable all-in-one textile system for real-time health monitoring in everyday wearable devices.