The non-physical-contact property of lasers poses significant challenges for the alignment procedure in precision engineering. Particularly in galvanometer-based laser processing systems, the requirement for multiple-step coordinate conversion further complicates the alignment procedure, thereby increasing the potential for error accumulation. To address the alignment issues during galvanometer laser scanning, this paper proposes an alignment-error-free solution for full-in-situ imaging and laser processing system, which eliminates the alignment error at the principal level by skipping the coordinate conversion and directly extracting angular coordinates for laser scanning from the captured images. Compared with the existing galvanometer-based laser processing systems, the main advantage of the proposed method is its ability to achieve alignment-error-free without requiring calibration, making it particularly suitable for small-batch, highly customized, and complex processing tasks. This system specifically facilitates in-line inspection, detection, and measurement during laser fabrications. Furthermore, two experimental cases in pan-semiconductor manufacturing, which includes flexible printed circuits (FPC) cutting and Micro-LEDs defect detection, have been conducted to demonstrate the validation of the proposed full-in-situ processing system. Correspondingly, the current experimental comparisons highlight the superiority of the proposed system for simultaneously achieving a maximum range of 27 mm × 27 mm and a minimum resolution of 0.412 µm, with a maximum processing error <15 µm. Demonstrations in detecting and processing the complex patterns illustrate its exceptional capabilities in alignment-error-free laser processing for precision manufacturing.