Patterning high-resolution multi-metal layers without using subtractive lithography poses a substantial challenge but is indispensable for the development of the modern electronics industry, especially flexible electronics. Herein, the general and feasible additive manufacturing approach is reported to selectively deposit high-resolution multi-metal patterns via surface-activation-localized electroless plating (SALEP) and enable the fabrication of 3-dimensional (3D) interconnections and high-performance organic thin-film transistor (OTFT) arrays for flexible electronics. The SALEP approach comprises the direct layer-by-layer deposition of multi-metal patterns interconnected by via holes, which are defined by the selective adsorption of palladium catalysts and a metallization process. The localized adsorption of the catalyst is guided by the difference in surface wettability and adsorbability caused by vacuum ultraviolet (VUV)-induced photochemical modification. The low-temperature and 3D approach enables miniaturization of flexible electrical circuits down to 1 µm in width; it also enables integration of an OTFT array on a flexible substrate. The fabricated OTFT array with multi-metal Cu/Ni/Au as contact electrodes exhibits a high hole mobility exceeding 10 cm² V⁻¹ s⁻¹, demonstrating the adaptability of the SALEP approach for the low-cost, high-efficiency, and scalable fabrication of high-performance flexible electronic devices.