This paper aims to investigate the effectiveness of using through-thickness stitching in suppressing impact-induced delamination growth in laminated composites. Low-velocity impact tests are conducted on unstitched and stitched specimens with varying stitch density and stitch thread thickness. Results show that stitching effectively bridges and arrests delamination crack, and reduces delamination growth up to 40%. It is also revealed that increasing stitch density is more effective (23% reduction) in minimising delamination area than increasing stitch thread thickness (8% reduction). A novel empirical-based Delamination Reduction Law (DRL) has been formulated to predict the delamination reduction in stitched composites due to impact loading. The DRL is further validated with numerous published literature results, which have demonstrated good consistency and excellent agreement with the prediction curve. The effectiveness of stitching in impact-induced delamination, which is primarily mode II and without stitch breakage, is compared and discussed with authors' previous work on mode I fracture delamination of stitched composites.