A novel in-textile photolithography method is introduced for creating precise and uniform metal patterns on porous textile structures. This technique enables high-resolution metal patterning with sub-100 μm precision, maintaining the textile's mechanical stability, washability, and permeability. The method involves polymer-assisted metal deposition (PAMD) followed by double-sided photolithography, allowing for the formation of well-defined, robust metal patterns within the textile scaffold. These patterns enable the construction of multifunctional, flexible, and highly integrated textile electronics with excellent performance and wearing comfort. The in-textile photolithography technique offers significant advantages over traditional on-textile patterning methods, including higher patterning resolution, better electrical conductivity, and enhanced mechanical robustness. The conductive patterns are permeated within the textile structure, enabling the creation of electronics on both sides of the fabric and facilitating multi-layer circuit construction. The method also provides excellent air and moisture permeability, as well as high bending and washing stability, with minimal changes in conductivity. The technique was demonstrated through the fabrication of a fully integrated biosensing headband for multiplexed sweat monitoring. This headband features ion-selective potentiometric sensors for pH, sodium, and potassium analysis, as well as enzymatic amperometric sensors for glucose and lactate tracking. The headband was able to monitor multiple sweat biomarkers in real-time with high accuracy and comfort, showing the potential of the in-textile photolithography method for practical wearable applications such as non-invasive health monitoring and human-machine interfaces. The in-textile photolithography method also enables the fabrication of high-performance micro-supercapacitors with enhanced areal capacitance. The technique allows for the creation of precise metal patterns with both linewidth and interspace down to 200 μm, ensuring successful device fabrication without short circuit issues. The method's ability to create conformal metal coatings on the fibers of the textile structure provides a large surface area for the deposition of electrochemically active materials, enhancing the performance of the devices. Overall, the in-textile photolithography method presents a promising approach for the development of permeable, high-performance, multifunctional, and highly integrated textile electronics suitable for wearable applications. The technique enables the creation of flexible, robust, and highly conductive metal patterns on porous textiles, opening new possibilities for the development of advanced textile-based electronics.A novel in-textile photolithography method is introduced for creating precise and uniform metal patterns on porous textile structures. This technique enables high-resolution metal patterning with sub-100 μm precision, maintaining the textile's mechanical stability, washability, and permeability. The method involves polymer-assisted metal deposition (PAMD) followed by double-sided photolithography, allowing for the formation of well-defined, robust metal patterns within the textile scaffold. These patterns enable the construction of multifunctional, flexible, and highly integrated textile electronics with excellent performance and wearing comfort. The in-textile photolithography technique offers significant advantages over traditional on-textile patterning methods, including higher patterning resolution, better electrical conductivity, and enhanced mechanical robustness. The conductive patterns are permeated within the textile structure, enabling the creation of electronics on both sides of the fabric and facilitating multi-layer circuit construction. The method also provides excellent air and moisture permeability, as well as high bending and washing stability, with minimal changes in conductivity. The technique was demonstrated through the fabrication of a fully integrated biosensing headband for multiplexed sweat monitoring. This headband features ion-selective potentiometric sensors for pH, sodium, and potassium analysis, as well as enzymatic amperometric sensors for glucose and lactate tracking. The headband was able to monitor multiple sweat biomarkers in real-time with high accuracy and comfort, showing the potential of the in-textile photolithography method for practical wearable applications such as non-invasive health monitoring and human-machine interfaces. The in-textile photolithography method also enables the fabrication of high-performance micro-supercapacitors with enhanced areal capacitance. The technique allows for the creation of precise metal patterns with both linewidth and interspace down to 200 μm, ensuring successful device fabrication without short circuit issues. The method's ability to create conformal metal coatings on the fibers of the textile structure provides a large surface area for the deposition of electrochemically active materials, enhancing the performance of the devices. Overall, the in-textile photolithography method presents a promising approach for the development of permeable, high-performance, multifunctional, and highly integrated textile electronics suitable for wearable applications. The technique enables the creation of flexible, robust, and highly conductive metal patterns on porous textiles, opening new possibilities for the development of advanced textile-based electronics.